TST: add categorical tests for DataFrame.equals

[ingo-stallknecht]

• closes #xxxx (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.
• If I used AI to develop this pull request, I prompted it to follow AGENTS.md.

What changes are proposed in this pull request?

This PR adds tests for DataFrame.equals with Categorical columns:

• Verifies that DataFrames are considered equal when values and categories are the same, even if the category order differs.
• Verifies that DataFrames are not equal when the category set differs.

This helps improve test coverage for equals on Categorical data.

How is this PR tested?

• New test in pandas/tests/frame/methods/test_equals.py

[ingo-stallknecht]

It looks like the micromamba cache step failed (ENOENT), which seems unrelated to this PR.
Let me know if I should rebase or push an update to retrigger CI.