-fmodules-ts is deprecated since clang16

[folliehiyuki]

I got the error when running test for the main please repo:

$ plz test --profile=alpine --exclude=py3 --exclude=python3 --exclude=no-musl --exclude=x86 --exclude=gold --exclude=py2 --exclude=java --exclude=e2e --log_file plz-out/log/test_build.log --log_file_level 4 --trace_file plz-out/log/trace.json

Build stopped after 150ms. 1 target failed:
    //test/cc_rules/clang/modules:_f1#interface
Error building target //test/cc_rules/clang/modules:_f1#interface: exit status 1
clang-16: error: the '-fmodules-ts' flag is deprecated and it will be removed in Clang 17; use '-std=c++20' or higher to use standard C++ modules instead [-Werror,-Wdeprecated-module-ts]