[test][MemDep] Correct the 'NOT' checks in the invalidation.ll test case. NFC

The MemoryDependenceAnalysis/invalidation.ll test case was using
  ; CHECK-NOT-AA-INVALIDATE:
but I think the intention was to use
  ; CHECK-AA-INVALIDATE-NOT:

Simply changing the checks like that would make the test fail.

The old statement that AA being stateless would result in nothing
to invalidate when doing invalidate<aa> is not true afaict.
It would be different if for example doing invalidate<basic-aa>, then
the AAManager isn't invalidated (and then neither memdep would be
invalidated). But when the AAManager itself is invalidated then we
should expect to find both "Invalidating analysis: AAManager" and
"Invalidating analysis: MemoryDependenceAnalysis" in the output.

Differential Revision: https://reviews.llvm.org/D146205