build(deps): update clang-format requirement from ==20.* to ==21.* (#167)

Updates the requirements on [clang-format](https://github.com/ssciwr/clang-format-wheel) to permit the latest version.
- [Release notes](https://github.com/ssciwr/clang-format-wheel/releases)
- [Commits](ssciwr/clang-format-wheel@v20.1.0...v21.1.0)

---
updated-dependencies:
- dependency-name: clang-format
  dependency-version: 21.1.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

scripts/requirements.txt

@@ -1 +1 @@
-clang-format==20.*
+clang-format==21.*