[NFCI] InstructionTest: trim `InstructionsTest.ShuffleMaskIsReplicationMask_*` complexity

These tests have pretty high O() complexity due to their nature,
which leads to potentially-long runtimes.

While in release build for me they took ~1 and ~2 sec,
as noted in https://reviews.llvm.org/D113214#inline-1080479
they take minutes in debug build.

Fine-tune the amount of permutations they deal with,
without affecting the test coverage. After this,
they take <~10ms each for me (in release build),
hopefully that is good-enough for debug build too.