[WIP] Begin testing on Python 3.12 and numpy 2.0-dev

[effigies]

Looks like scipy switched to a new nightly repository about a month ago: https://anaconda.org/scientific-python-nightly-wheels

Starting by running current tests. Will add Python 3.12 if those pass.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.10% ⚠️

Comparison is base (8fea2a8) 92.16% compared to head (f144e88) 92.07%.

❗ Current head f144e88 differs from pull request most recent head 30ba615. Consider uploading reports for the commit 30ba615 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1242      +/-   ##
==========================================
- Coverage   92.16%   92.07%   -0.10%     
==========================================
  Files          98       98              
  Lines       12370    12368       -2     
  Branches     2542     2540       -2     
==========================================
- Hits        11401    11388      -13     
- Misses        646      656      +10     
- Partials      323      324       +1     

Files Changed	Coverage Δ
nibabel/filebasedimages.py	97.29% <100.00%> (ø)

... and 8 files with indirect coverage changes

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