Fix dogfood PR artifact retrieval for failed aggregate builds

[jfversluis]

Note

Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Description

Updates eng/scripts/get-maui-pr.sh and eng/scripts/get-maui-pr.ps1 so users can still apply PR package artifacts when the aggregate maui-pr build is red because of unrelated CI legs, as long as the package-producing artifacts exist for the current PR commit.

Changes

• Treat a red aggregate maui-pr build as a warning instead of an immediate abort.
• Keep PackageArtifacts as the hard gate before downloading/applying packages.
• Filter AzDO fallback builds to the current PR head/merge context using triggerInfo.pr.sourceSha, sourceVersion, and the PR merge SHA.
• Warn when Pack macOS or Pack Windows timeline records do not report success.
• Update troubleshooting text to refer to completed maui-pr builds with PackageArtifacts rather than green checks.

Validation

• bash -n eng/scripts/get-maui-pr.sh
• PowerShell parser validation for eng/scripts/get-maui-pr.ps1
• git diff --check
• Local throwaway MAUI projects under /Volumes/NieuwVolume/maui-pr-artifact-verification-20260616101523:
  • PR #35805: red aggregate build 1461390, PackageArtifacts present, pack jobs succeeded; Bash and PowerShell scripts applied package 10.0.80-ci.pr35805.26312.37; dotnet restore succeeded.
  • PR #35923: green aggregate build path applied package 10.0.80-ci.pr35923.26315.57; dotnet restore succeeded.
  • PR #35626: missing PackageArtifacts failed before mutating the project.
  • PR #999999: nonexistent PR failed cleanly during PR lookup.
  • Wrong-SHA harness for PR #35805: refused to use older completed builds when none matched the requested head/merge commit.

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 35939

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 35939"