fix(ci): set git identity before re-merging target branch in PR workflows

[IvanaGyro]

Summary

Several PR workflows re-merge the base branch at job start so CI tests against the latest target branch, rather than a stale merge-preview commit:

git fetch origin ${{ github.event.pull_request.base.ref }}
git merge --no-edit origin/${{ github.event.pull_request.base.ref }}

When the base branch has advanced since GitHub computed the PR's merge-preview commit, this is a non-fast-forward merge, so git needs to create a real merge commit — which requires a committer identity. Ubuntu-hosted runners don't have one configured, while macOS-hosted runners do (a ~/.gitconfig is baked into that image), so this fails intermittently and only on Ubuntu with:

Committer identity unknown
fatal: empty ident name (for <runner@...>) not allowed

This was observed on PR #987, where BuildAndTest-ubuntu-latest, DownstreamFindPackage, and Formatting Check all failed this way after master advanced mid-run, while the macOS legs of the same run succeeded.

release_pypi.yml already sets a bot git identity before this same merge step. This PR applies the identical fix to the other four workflows that have the same unguarded pattern:

• ci-cmake_tests.yml
• ci-downstream-find-package.yml
• clang-format-check.yml
• conda_build.yml

Test plan

• CI passes on this PR (Ubuntu legs in particular)

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Generated by Claude Code

[gemini-code-assist]

Note

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 30.92%. Comparing base (b5db6b8) to head (fde8d73).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1002   +/-   ##
=======================================
  Coverage   30.92%   30.92%           
=======================================
  Files         229      229           
  Lines       34760    34760           
  Branches    14398    14398           
=======================================
  Hits        10749    10749           
  Misses      16708    16708           
  Partials     7303     7303           

Flag	Coverage Δ
cpp	30.43% <ø> (ø)
python	59.41% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
C++ backend	32.25% <ø> (ø)
Python bindings	17.28% <ø> (ø)
Python package	59.41% <ø> (ø)

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[pcchen]

Thanks for this, @IvanaGyro — it's a correct fix. It's essentially identical to #1007 (same 4 workflow files, same git config user.name/user.email lines before the target-branch merge; the only difference is comment wrapping/indentation). To avoid duplicate changes we're going with #1007 — could you close this one in favor of it? The fix itself is equally valid either way.

Posted by Claude Code on behalf of @pcchen

[pcchen]

I will close this.