[llvm] [Github] Bump clang-format to 21.1.0 (PR #155660)

[via llvm-commits]

================
@@ -55,7 +55,7 @@ jobs:
       - name: Install clang-format
         uses: aminya/setup-cpp at 17c11551771948abc5752bbf3183482567c7caf0 # v1.1.1
         with:
-          clangformat: 20.1.8
+          clangformat: 21.1.0
----------------
owenca wrote:

```suggestion
          clangformat: 21.1.0 # Update this to the first and last versions of a release cycle
```

https://github.com/llvm/llvm-project/pull/155660