.github: workflows: Add C++ linter

[melvo]

PR check list:

• [x] Document your code
• [x] Add \since QXmpp 1.X, QXMPP_EXPORT
• [x] Fix doxygen warnings (see log when building with -DBUILD_DOCUMENTATION=ON)
• [x] Update doc/doap.xml
• [x] Add unit tests
• [x] Format the code: Run clang-format -i src/<edited-file(s)> tests/<edited-file(s)>

[melvo]

The action does not support clang-format-15 (only clang-format-14) but the linting tool does.

[codecov[bot]]

Codecov Report

Base: 68.36% // Head: 68.47% // Increases project coverage by +0.11% :tada:

Coverage data is based on head (9fa6206) compared to base (befab2f). Patch has no changes to coverable lines.

:exclamation: Current head 9fa6206 differs from pull request most recent head ba24679. Consider uploading reports for the commit ba24679 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #491 +/- ## ========================================== + Coverage 68.36% 68.47% +0.11% ========================================== Files 298 292 -6 Lines 25869 25653 -216 ========================================== - Hits 17685 17567 -118 + Misses 8184 8086 -98 ``` | [Impacted Files](https://codecov.io/gh/qxmpp-project/qxmpp/pull/491?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project) | Coverage Δ | | |---|---|---| | [src/client/QXmppEntityTimeManager.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/491?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2NsaWVudC9RWG1wcEVudGl0eVRpbWVNYW5hZ2VyLmNwcA==) | `12.90% <0.00%> (-2.73%)` | :arrow_down: | | [src/client/QXmppVersionManager.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/491?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2NsaWVudC9RWG1wcFZlcnNpb25NYW5hZ2VyLmNwcA==) | `26.08% <0.00%> (-2.18%)` | :arrow_down: | | [src/base/QXmppDiscoveryIq.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/491?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2Jhc2UvUVhtcHBEaXNjb3ZlcnlJcS5jcHA=) | `84.61% <0.00%> (-0.18%)` | :arrow_down: | | [tests/qxmppmessage/tst\_qxmppmessage.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/491?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-dGVzdHMvcXhtcHBtZXNzYWdlL3RzdF9xeG1wcG1lc3NhZ2UuY3Bw) | `94.82% <0.00%> (-0.10%)` | :arrow_down: | | [src/base/QXmppMessage.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/491?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2Jhc2UvUVhtcHBNZXNzYWdlLmNwcA==) | `98.31% <0.00%> (-0.04%)` | :arrow_down: | | [src/omemo/QXmppOmemoManager\_p.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/491?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL29tZW1vL1FYbXBwT21lbW9NYW5hZ2VyX3AuY3Bw) | `5.00% <0.00%> (-0.01%)` | :arrow_down: | | [src/base/QXmppMessage.h](https://codecov.io/gh/qxmpp-project/qxmpp/pull/491?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2Jhc2UvUVhtcHBNZXNzYWdlLmg=) | `100.00% <0.00%> (ø)` | | | [src/client/QXmppClient.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/491?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2NsaWVudC9RWG1wcENsaWVudC5jcHA=) | `59.80% <0.00%> (ø)` | | | [tests/qxmppjingleiq/tst\_qxmppjingleiq.cpp](https://codecov.io/gh/qxmpp-project/qxmpp/pull/491?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-dGVzdHMvcXhtcHBqaW5nbGVpcS90c3RfcXhtcHBqaW5nbGVpcS5jcHA=) | `100.00% <0.00%> (ø)` | | | [src/client/QXmppMamManager.h](https://codecov.io/gh/qxmpp-project/qxmpp/pull/491?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project#diff-c3JjL2NsaWVudC9RWG1wcE1hbU1hbmFnZXIuaA==) | | | | ... and [14 more](https://codecov.io/gh/qxmpp-project/qxmpp/pull/491?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project) | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=qxmpp-project)

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[melvo]

clang-format-15 is supported now. Result: Only src/client/QXmppFileSharingManager.cpp seems to need adjustments or maybe .clang-format.

[melvo]

@lnjX This can be reviewed now.