[Github] Make PR formatting job only run with C/C++ changes (#69556)

Currently the PR formatting job only runs clang-format. There isn't a
lot of utility in running it if there aren't any C/C++ changes as there
will be nothing to format. This isn't super noisy currently as the job
doesn't fail if there aren't any C/C++ changes, but it's a bit of a
waste.

In addition, this patch names the code formatting job "Check C++
Formatting" to make it clear that this job only checks C/C++ formatting
rather than Python formatting/other languages.