Temp fix for broken detectron2 import

[patrickvonplaten]

What does this PR do?

Detectron2 is currently broken on master as can be seen here:

• detectron2/utils/tracing.py", line 5, in <module> from torch.fx._symbolic_trace import is_fx_tracing as is_fx_tracing_current ImportError: cannot import name 'is_fx_tracing' from 'torch.fx._symbolic_trace' facebookresearch/detectron2#4489
• ImportError: cannot import name 'is_fx_tracing' from 'torch.fx._symbolic_trace' facebookresearch/detectron2#4487

In order to not affect all kinds of tests, we add a temporary fix here that will only let LayoutLMv2 fail that is dependent on detectron2, but other tests that just import the layoutlmv2 module won't be affected so that the Circle CI stays green

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[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[simonhollis]

Hi @patrickvonplaten . Please review the thread at facebookresearch/detectron2#4489 and let me know if the landed change means we can now revert this temporary fix. Thanks.