Avoid spurious deprecation warning in CustomDist

[ricardoV94]

Description

The warning is causing the CI in pymc-experimental to fail pymc-devs/pymc-experimental#352

Also allow multivariate CustomDist to be created when signature suffices to infer core shape.

Related Issue

• Closes #
• Related to #

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):

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📚 Documentation preview 📚: https://pymc--7391.org.readthedocs.build/en/7391/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.19%. Comparing base (b496127) to head (b2f3c48).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7391   +/-   ##
=======================================
  Coverage   92.19%   92.19%           
=======================================
  Files         103      103           
  Lines       17214    17208    -6     
=======================================
- Hits        15870    15865    -5     
+ Misses       1344     1343    -1     

Files	Coverage Δ
pymc/distributions/custom.py	95.54% <100.00%> (+1.08%)	⬆️

... and 1 file with indirect coverage changes