[3.0] Added a workaround for PR checks from forked repos.

[PawelWMS]

Merge Checklist

All boxes should be checked before merging the PR (just tick any boxes which don't apply to this PR)

• The toolchain has been rebuilt successfully (or no changes were made to it)
• The toolchain/worker package manifests are up-to-date
• Any updated packages successfully build (or no packages were changed)
• Packages depending on static components modified in this PR (Golang, *-static subpackages, etc.) have had their Release tag incremented.
• Package tests (%check section) have been verified with RUN_CHECK=y for existing SPEC files, or added to new SPEC files
• All package sources are available
• cgmanifest files are up-to-date and sorted (./cgmanifest.json, ./toolkit/scripts/toolchain/cgmanifest.json, .github/workflows/cgmanifest.json)
• LICENSE-MAP files are up-to-date (./SPECS/LICENSES-AND-NOTICES/data/licenses.json, ./SPECS/LICENSES-AND-NOTICES/LICENSES-MAP.md, ./SPECS/LICENSES-AND-NOTICES/LICENSE-EXCEPTIONS.PHOTON)
• All source files have up-to-date hashes in the *.signatures.json files
• sudo make go-tidy-all and sudo make go-test-coverage pass
• Documentation has been updated to match any changes to the build system
• Ready to merge

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Summary

Adding a workaround for the issue where pip install would fail if it was ran on a PR check build when the PR has been opened from a fork of the upstream repository.

Does this affect the toolchain?

No.

Associated issues

• IcM ticket.

Test Methodology

• Dummy PR from a fork: [DELETE ME] pip install test #14220. Its PR check made it through the pip install step.

[aaruag]

/azurepipelines run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[CBL-Mariner-Bot]

Auto cherry-pick results:

• 3.0-dev ✅ -> [AUTO-CHERRYPICK] [3.0] Added a workaround for PR checks from forked repos. - branch 3.0-dev #14255

Auto cherry-pick pipeline run -> https://dev.azure.com/mariner-org/mariner/_build/results?buildId=863479&view=results