[quant][fx] Fix weight_dtype and bias_dtype backend_config checks (#86719)
Summary:
This PR adds checks for the existence of "weight_dtype" and "bias_dtype" in the node_name_to_dtype dictionary before accessing it,
the corner case is hit when we check the compatibility of qconfig and backend_config for weight and bias that appears before activation (e.g. torch.addmm)
Test Plan:
python test/test_quantization.py -k test_backend_config_check_for_weight_and_bias
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Pull Request resolved: https://github.com/pytorch/pytorch/pull/86719
Approved by: https://github.com/andrewor14
