Auto merge of #109521 - tmiasko:const-prop-validation, r=wesleywiser

Don't validate constants in const propagation

Validation is neither necessary nor desirable.

The constant validation is already omitted at mir-opt-level >= 3, so there there are not changes in MIR test output (the propagation of invalid constants is covered by an existing test in tests/mir-opt/const_prop/invalid_constant.rs).

Author: bors