[llvm] [Github] Make prune-unused-branches workflow save branch list (PR #181194)

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github-actions[bot] wrote:

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:warning: Python code formatter, darker found issues in your code. :warning:

<details>
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You can test this locally with the following command:
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``````````bash
darker --check --diff -r origin/main...HEAD .github/workflows/prune-unused-branches.py
``````````

:warning:
The reproduction instructions above might return results for more than one PR
in a stack if you are using a stacked PR workflow. You can limit the results by
changing `origin/main` to the base branch/commit you want to compare against.
:warning:

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View the diff from darker here.
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``````````diff
--- prune-unused-branches.py	2026-02-12 17:49:16.000000 +0000
+++ prune-unused-branches.py	2026-02-12 17:55:18.767891 +0000
@@ -134,11 +134,13 @@
     print(f"Found {len(user_branches_from_prs)} user branches associated with PRs")
     user_branches_to_remove = get_user_branches_to_remove(
         user_branches, user_branches_from_prs
     )
     print(f"Deleting {len(user_branches_to_remove)} user branches.")
-    generate_patches_for_all_branches(user_branches_to_remove, os.path.join(output_dir, "patches"))
+    generate_patches_for_all_branches(
+        user_branches_to_remove, os.path.join(output_dir, "patches")
+    )
     delete_branches(user_branches_to_remove)
 
 
 if __name__ == "__main__":
     main(os.environ["GITHUB_TOKEN"])

``````````

</details>


https://github.com/llvm/llvm-project/pull/181194