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

[Hans Wennborg via cfe-commits]

zmodem 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.)

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