[llvm] [docs] Make rebase advice more explicit for cases where pre-commit CI is failing (PR #76704)

[via llvm-commits]

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@@ -105,7 +105,9 @@ branch that's the root of the Pull Request during the review. This action will
 make the context of the old changes and comments harder to find and read.
 
 Sometimes, a rebase might be needed to update your branch with a fix for a test
-or in some dependent code.
+or in some dependent code. This is especially encouraged if it turns out that
+the upstream base commit used for your branch had test failures, meaning the
+pre-commit CI results are not useful.
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itrofimow wrote:

Chiming in as the author of aforementioned https://github.com/llvm/llvm-project/pull/65534: I've decided to go with `git merge` instead of `git rebase` from now on exactly due to the UI reason -- i too find it much easier to navigate through changes this way, when imo rebasing just breaks history.

https://github.com/llvm/llvm-project/pull/76704