[clang] [clang][unittests] Fix flaky PerformPendingInstantiations nesting in TimeProfilerTest (PR #193717)

[Paweł Bylica via cfe-commits]

chfast wrote:

> (Please avoid force-pushing changes: https://llvm.org/docs/GitHub.html#updating-pull-requests it makes it hard to see what changed from previous commits.)

Sorry, that was only the main rebase.
Do you think this can be merged or we are waiting for more reviews?

https://github.com/llvm/llvm-project/pull/193717