[clang-format] [C++20] [Module] clang-format couldn't recognize partitions

https://bugs.llvm.org/show_bug.cgi?id=52517

clang-format is butchering modules, this could easily become a barrier to entry for modules given clang-formats wide spread use.

Prevent the following from adding spaces around the  `:`  (cf was considering the ':' as an InheritanceColon)

Reviewed By: HazardyKnusperkeks, owenpan, ChuanqiXu

Differential Revision: https://reviews.llvm.org/D114151