[clang-tidy] Ignore template instantiations in modernize-use-using

The test I'm adding passes without the change due to the deduplication logic in
ClangTidyDiagnosticConsumer::take(). However this bug manifests in our internal
integration with clang-tidy.
I've verified the fix by locally changing LessClangTidyError to consider
replacements.

llvm-svn: 347470