Add inter branch merge flow config for 9.0 RC branches

[carlossanlop]

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[carlossanlop]

No CI validation for this change. Will merge right away to get this included in the 9.0 branch.

[carlossanlop]

This isn't working. We have had some new commits in the release/9.0-rc1 branch but I don't see any PRs created to autoflow those commits to the released/9.0 branch. What am I missing, @jkoritzinsky @mmitche @hoyosjs @f-alizada?

[carlossanlop]

Yeah, it's not running: https://github.com/dotnet/runtime/actions/workflows/inter-branch-merge-flow.yml

What I suspect is that it won't work unless it's in both release/9.0-rc1 and release/9.0.

I was hoping it would get autotriggered by just existing in release/9.0-rc1. I'll backport it to the remaining branch and see if that does it.

[carlossanlop]

Actually, I snapped both release/9.0 and release/9.0-rc1 after merging this PR, meaning all the necessary branches already include this.

[f-alizada]

@carlossanlop I have created the PR #106614 which adds the workflow file to the branch.
This is the reason it is not triggering on merges into the branches.
Adding the workflow to the main here: #106616 as well to avoid such situations in future.