Make error message more informative
Author: Atomnp
Pull request: yes

# What does this PR do?
Make error message more descriptive by adding one word, changes the message `The hidden size ({config.hidden_size}) is not a multiple of the number of attention` to `The hidden size ({config.hidden_size}) is not a multiple of the number of attention heads` in the previous error message, the word "head" was missing

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Comments:
_The documentation is not available anymore as the PR was closed or merged._