[LoopVersioning] Invalidate SCEV for phi if new values are added.

After 20d798bd, SCEV looks through PHIs with a single incoming
value. This means adding a new incoming value may change the SCEV for a
phi. Add missing invalidation when an existing PHI is reused during
LoopVersioning. New incoming values will be added later from the
versioned loop.

Similar issues have been fixed by also adding missing invalidation.

Fixes #57825.

Note that the test case unfortunately requires running loop-vectorize
followed by loop-load-elimination, which does the actual versioning. I
don't think it is possible to reproduce the failure without that
combination.