Skip `test_export_to_onnx` for `LongT5` if `torch` < 1.11
# What does this PR do?

With torch `1.10`, We get some exception from C++ file.
```bash
Exception raised from index_select_out_cpu_ at ../aten/src/ATen/native/TensorAdvancedIndexing.cpp:887 (most recent call first):
frame #0: c10::Error::Error(c10::SourceLocation, std::string) + 0x42 (0x7f60b7f4dd62 in /home/yih_dar_huggingface_co/miniconda3/envs/py39/lib/python3.9/site-packages/torch/lib/libc10.so)
```
Skip this test for torch < 1.11: **Make past CI clean**


P.S. this test is only defined for 3 models (T5, LongT5 and FSMT), but skipped (without any condition) for T5 and FSMT.
It should be fine to remove this test, and rely on `tests/onnx`.
_The documentation is not available anymore as the PR was closed or merged._