clang-format in CI

[germasch]

So I think I figured out why I still get mis-formatted files even though I was using git clang-format: By default, it won't check .inl, and .tcc files.

I did this locally:

git config clangformat.extensions "c,h,cc,cp,cpp,c++,cxx,hpp,inl,tcc"

and I think this also should be done in the CI, since the CI didn't complain about my misformatted .inl and .tcc files.