[BasicAA] Handle assumes with operand bundles

This fixes a regression reported on D99022: If a call has operand
bundles, then the inaccessiblememonly attribute on the function
will be ignored, as operand bundles can affect modref behavior in
the general case. However, for assume operand bundles in particular
this is not the case.

Adjust getModRefBehavior() to always report inaccessiblememonly
for assumes, regardless of presence of operand bundles.