[VPlan] Don't mark VPBlendRecipe as phi-like.

VPBlendRecipes don't get lowered to phis and usually do not appear at
the beginning of blocks, due to their masks appearing before them.

This effectively relaxes an over-eager verifier message.

Fixes https://github.com/llvm/llvm-project/issues/88297.
Fixes https://github.com/llvm/llvm-project/issues/88804.