Fix warning message since m2w64-toolchain is no longer installable

[maresb]

For more context, see the discussion in:
conda-forge/pytensor-suite-feedstock#133 (comment)

Description

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://pytensor--1238.org.readthedocs.build/en/1238/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.99%. Comparing base (e7dec4d) to head (c897219).
Report is 157 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1238   +/-   ##
=======================================
  Coverage   81.99%   81.99%           
=======================================
  Files         188      188           
  Lines       48567    48567           
  Branches     8677     8677           
=======================================
  Hits        39823    39823           
  Misses       6581     6581           
  Partials     2163     2163           

Files with missing lines	Coverage Δ
pytensor/configdefaults.py	73.46% <ø> (ø)

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