[`./bin/test`] Allow skipping clone of `swift-docc` and `swift-docc-render-artifact`

[bitjammer]

From https://github.com/apple/swift-docc-plugin/pull/21#discussion_r929419898

In some scenarios, running swift-docc-plugin tests against the built-in docc in the installed toolchain could save time. Add an option to ./bin/test to skip cloning swift-docc and swift-docc-render-artifact and setting the environment variables to use those.

Behavior:

If --skip-building-upstream-docc (or perhaps an environment variable) is set:

• Don't set the following:
  • SWIFT_DOCC_ROOT
  • SWIFT_DOCC_RENDER_ARTIFACT_ROOT
  • SWIFT_DOCC_BRANCH
  • SWIFT_DOCC_RENDER_ARTIFACT_BRANCH
• Don't clone swift-docc or swift-docc-render-artifact
• Also don't set:
  • DOCC_EXEC
  • DOCC_HTML_DIR

See the above mentioned pull request for new code that should be skipped in this case.

[A-N-uraag]

Hi @bitjammer, can I work on this? I went through the mentioned PR and I now have a clear idea on what needs to be done.

[bitjammer]

Of course, that’s why it’s here! Thank you for taking it on. Please have a go and let me know if you have any questions.

[A-N-uraag]

Hi @bitjammer, I raised a PR. I used the approach to use an env variable. Hope that's fine.

[A-N-uraag]

Hi @bitjammer, just sending a little nudge to bump up the PR in your inbox. Thanks.

[bitjammer]

Thank you! I will have a look at this today.

[bitjammer]

Nice work @A-N-uraag, thank you.