[InstCombine] Don't handle constants in de morgan folds (PR63791)

If the and/or operand is an immediate constant, it will get folded
away anyway. Don't try to freely invert those operands.

A particularly degenerate case of this arises when both operands
are constant and the result is a constant, in which case we try
to invert users of a constant, resulting in an assertion failure.

Fixes https://github.com/llvm/llvm-project/issues/63791.