NFC add a new precommit test case for PPCMIpeephole (#90656)

Add pre-commit MIR test for PR "[Promote Pseudo Opcode from 32-bit to
64-bit after eliminating the extsw instruction in PPCMIPeepholes
optimization](https://github.com/llvm/llvm-project/pull/85451)" which
fixes bug reported in the issue "[Inconsistent Output at -O1 and -O2
Optimization Levels on PowerPC64 Due to Complex Type Casting and Nested
Loop Structure](https://github.com/llvm/llvm-project/issues/71030)".