CI: Fix clang-format if path has spaces

If the path to clang-format has spaces, as might occur when testing
locally with a version not covered in this script, it will fail. Enclose
the call to clang-format in quotes to prevent this failure.

CI/check-format.sh

@@ -55,4 +55,4 @@ find . -type d \( \
     -name '*.mm' -or \
     -name '*.c' -or \
     -name '*.cpp' \
- | xargs -L100 -P ${NPROC} ${CLANG_FORMAT} ${VERBOSITY} -i -style=file -fallback-style=none
+ | xargs -L100 -P ${NPROC} "${CLANG_FORMAT}" ${VERBOSITY} -i -style=file -fallback-style=none