Fix NumPy warning in test_functions

[swt2c]

Fixes the below warning about integer conversion by using astype() - overflow seems OK/desired in this case.

tests/test_functions.py:290
  /home/runner/work/pyqtgraph/pyqtgraph/tests/test_functions.py:290: DeprecationWarning: NumPy will stop allowing conversion of out-of-bound Python integers to integer arrays.  The conversion of -1 to uint32 will fail in the future.
  For the old behavior, usually:
      np.array(value).astype(dtype)`
  will give the desired result (the cast overflows).
    np.arange(6, dtype=dtype), np.arange(0, -6, step=-1, dtype=dtype), 'all',

[swt2c]

The test failures seem to be unrelated. In fact, they seem possibly related to Python 3.11.4?

[j9ac9k]

Thanks for fixing this; I'll investigate the failures today!

[swt2c]

I think the failures might actually be due to this CPython bug: python/cpython#105497

[j9ac9k]

ahh, yeah saw some chatter about this on the pyqt mail list... looks like it will be fixed in 3.11.5. I'm good with merging as is, should probably put a note on the README about an incompatibility with PyQt/Python 3.11.4, but that's out of scope for this PR.

@swt2c do you have a preferred method I can reach out to you privately? If you have some time, would you mind sending me a message on your preferred platform? My contact info is on my github profile page

[swt2c]

@j9ac9k sent you an email.

[j9ac9k]

Thanks for the PR @swt2c this LGTM, merging!