Run Evoformer tests sequentially (#7810)
Evoformer tests fail when we run them in parallel with other tests.
```
RuntimeError: Cannot re-initialize CUDA in forked subprocess.
```
This PR adds `@pytest.mark.sequential` to the tests.
See the full test log for details:
https://github.com/deepspeedai/DeepSpeed/actions/runs/21303530770/job/61326548592
Signed-off-by: Masahiro Tanaka <mtanaka@anyscale.com>
