[clang] [Sema] Fix crash on invalid operator template-id (PR #181404)

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nehaGautam07 wrote:

> @zwuis these failures look legitimate - it's the new test not producing the expected errors. I'd swear this passed the bots though - maybe revert in the short term?
> 
> @nehaGautam07 If you can work out what's failing we should be able to just land the correction

Thanks, I’ll investigate and update with a fix.

https://github.com/llvm/llvm-project/pull/181404