Fix 3 failing slow bart/blender tests
3 of these were simple fixes.
+ 1 typo in blenderbot
+ 2 BART failures changed by new `assert_tensors_close` helper fn checking shapes more aggressively. Output shapes have not changed.

The fourth failure is a bit harder to verify
Blenderbot 3b was OOMing
before fix: 11.4 GB
After: 6.4 GB
Why:  going to fp16 before going to cuda
I don't think the change can possibly harm, so I will merge without review. cc @sgugger @LysandreJik 