Transformers: fix src and key padding mask bool regression (#96009)
Summary: fix src and pad mask bool regression
This fixes a regression introduced previously with #92733. That PR unified testing of masks to remove Byte Tensors as permissible mask, introduced mask compatibility check, and mask conversion to FP mask. The problem addressed in this PR was that after the first mask had been converted, a check for mask compatibility would fail.
Test Plan: sandcastle & github
Differential Revision: D43782858
Fixes https://github.com/pytorch/pytorch/issues/95702
Pull Request resolved: https://github.com/pytorch/pytorch/pull/96009
Approved by: https://github.com/malfet
