Fix broken GemmRewriteTest.BF16GemmCodeGen on Hopper.
Fix broken GemmRewriteTest.BF16GemmCodeGen on Hopper.

This was broken by https://github.com/openxla/xla/commit/4e09e73967247dc0226fec1021bf794d80614059.

The issue is that the optimized HLO was changed by having a native BF16 multiply, so the filecheck string had to be changed. Because the multiply is done in BF16 instead of FP32, the tolerance must also be lowered.
