Fix numpy 1.25 deprecation warnings - #14671

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Well before this PR only 2 deprecation warnings were reported (e.g., https://github.com/astropy/astropy/actions/runs/4768585591/jobs/8478077374). Those were fixed by this PR, but now's there's a whole bunch more.

I've updated this PR to fix all the new numpy 1.25 deprecations (and changed error message):

• Conversion of an array with ndim > 0 to a scalar is deprecated
• ValueError: setting an array element with a sequence.
• A ValueError message was changed

Most of the new warnings came from the models subpackage. The base Model.__call__ method wraps the model evaluate methods, but it also turns scalar inputs into arrays before calling evaluate. So in some cases evaluate expects a scalar, but gets an array.