use no_grad() consistently for testing transformer trace construction (#106523)
Summary: check trace runs with no_grad() and grad or not impacts transformer trace construction. use no_grad() consistently
Test Plan:
sandcastle and github ci
```
buck2 run mode/opt mode/inplace //caffe2/test:test_jit_cuda -- --regex test_scriptmodule_transformer_cuda
```
Differential Revision: D48020889
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106523
Approved by: https://github.com/davidberard98
