Only check c/c++ files with clang-format pre-commit

[alexander-novo]

Description

Fixes #120

Proposed changes

Make sure to only run clang-format on C/C++ files.

Checklist

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• All tests pass.
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows GridKit™ style guidelines.
• There are unit tests for the new code.
• The new code is documented.
• The feature branch is rebased with respect to the target branch.

Further comments