[clang] [clang][analysis] Fix flaky clang/test/Analysis/live-stmts.cpp test (PR #126913)

[Balazs Benics via cfe-commits]

steakhal wrote:

> @steakhal : Sure I can do some tests if you come up with a fix. Right now, with an EXPENSIVE_CHECKS build it fails in 30-40% of the runs for me so it should be pretty quick to see if a fix works or not. I've never seen it fail without EXPENSIVE_CHECKS.

I could reproduce the flakyness on my system using expensive checks. Thanks for the hint.

https://github.com/llvm/llvm-project/pull/126913