Only use --verify-config to check config

[mattlangford]

This is very similar to #93, but does the same move in the actual clang tidy script.

I verified that this let clang tidy run in a private repo (where before it would return no errors). It also errors out when there are config errors

[erenon]

Thanks!

[dotnwat]

@mattlangford

I observe that clang-tidy returns 0 success code even when there are verification errors. This is using clang-20.

So we probably should check for the success output "No config errors found." (or fix clang-tidy). Otherwise, config verification failure still just passes through as success it seems.

$ bazel-out/k8-fastbuild/bin/external/toolchains_llvm++llvm+current_llvm_toolchain/clang-tidy --quiet --verify-config; echo $?
/home/nwatkins/src/redpanda/.clang-tidy:14:5: error: Unexpected token in Key Value.
    asdf
    ^
Error parsing /home/nwatkins/src/redpanda/.clang-tidy: Invalid argument
/home/nwatkins/src/redpanda/.clang-tidy:14:5: error: Unexpected token in Key Value.
    asdf
    ^
Error parsing /home/nwatkins/src/redpanda/.clang-tidy: Invalid argument
No config errors detected.
0

[mattlangford]

Good catch @dotnwat, the changes in #95 seem to help with that!