The docstring of _in() says the ValueError would contain these, however
it didn't. Adding said arguments enables uniform processing of
ValueErrors raised by validators. One might for example want to extract
the attr.name and the value that raised the error to show a custom, more
user-friendly error message.

Since the error message isn't the only error argument anymore (but
should still suffice to test functionality), it was necessary to only
assert against the first argument.

I thought I could get away with lazyness but it's better to do it the
right way. The tests now check the full error signature.

This should sufficiently summarize the changes.

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This should allow for backwards-compatibility.

…error=True"

This should sufficiently test the verbose signature.

I noticed that the number didn't correspond to the PR #, so I renamed
the file. Also modified the content to properly reflect the changes.

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…ewlines

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This reverts commit d7cfbd3.

This reverts commit d40b6e4.

This reverts commit 1b6228a

This reverts commit 562eb51

…e_value_error=True""

This reverts commit 8a0d27e.

…rror=False""

This reverts commit 32cc097.

… and somehow reappeared during revert horror