[projmgr] Fix relative `--output` option

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 80.00000% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 63.20%. Comparing base (2523118) to head (d8e22c7). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1498 +/- ## ========================================== + Coverage 63.18% 63.20% +0.02% ========================================== Files 162 162 Lines 30708 30731 +23 Branches 18825 18841 +16 ========================================== + Hits 19403 19424 +21 - Misses 7533 7534 +1 - Partials 3772 3773 +1 ``` | [Flag](https://app.codecov.io/gh/Open-CMSIS-Pack/devtools/pull/1498/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Open-CMSIS-Pack) | Coverage Δ | | |---|---|---| | [projmgr-cov](https://app.codecov.io/gh/Open-CMSIS-Pack/devtools/pull/1498/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Open-CMSIS-Pack) | `80.29% <80.00%> (+0.02%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Open-CMSIS-Pack#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files](https://app.codecov.io/gh/Open-CMSIS-Pack/devtools/pull/1498?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Open-CMSIS-Pack) | Coverage Δ | | |---|---|---| | [tools/projmgr/src/ProjMgr.cpp](https://app.codecov.io/gh/Open-CMSIS-Pack/devtools/pull/1498?src=pr&el=tree&filepath=tools%2Fprojmgr%2Fsrc%2FProjMgr.cpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Open-CMSIS-Pack#diff-dG9vbHMvcHJvam1nci9zcmMvUHJvak1nci5jcHA=) | `79.81% <100.00%> (ø)` | | | [tools/projmgr/src/ProjMgrWorker.cpp](https://app.codecov.io/gh/Open-CMSIS-Pack/devtools/pull/1498?src=pr&el=tree&filepath=tools%2Fprojmgr%2Fsrc%2FProjMgrWorker.cpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Open-CMSIS-Pack#diff-dG9vbHMvcHJvam1nci9zcmMvUHJvak1ncldvcmtlci5jcHA=) | `86.63% <100.00%> (ø)` | | | [tools/projmgr/test/src/ProjMgrUnitTests.cpp](https://app.codecov.io/gh/Open-CMSIS-Pack/devtools/pull/1498?src=pr&el=tree&filepath=tools%2Fprojmgr%2Ftest%2Fsrc%2FProjMgrUnitTests.cpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Open-CMSIS-Pack#diff-dG9vbHMvcHJvam1nci90ZXN0L3NyYy9Qcm9qTWdyVW5pdFRlc3RzLmNwcA==) | `79.40% <77.77%> (+0.05%)` | :arrow_up: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/Open-CMSIS-Pack/devtools/pull/1498/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Open-CMSIS-Pack)