fix: remove _warn_on_old_setuptools() that warns incorrectly with custom build-backends

[RonnyPfannschmidt]

Summary

• Remove _warn_on_old_setuptools() which checked setuptools.__version__ at import time and emitted a RuntimeWarning when the major version was < 61
• With custom build-backends (e.g. qtile's), setuptools.__version__ can return the project version rather than setuptools' actual version, causing a spurious warning
• The minimum setuptools version is already enforced via build-system requires (setuptools>=77.0.3), making this runtime check redundant

Fixes #1192

Test plan

• Existing integration tests pass (uv run pytest setuptools-scm/testing_scm/test_integration.py -n12 — 49 passed)
• Pre-commit hooks pass (ruff, mypy, codespell, etc.)
• Removed the now-unnecessary testwarn_on_broken_setuptools test

Made with Cursor

[Copilot]

Pull request overview

Removes an import-time setuptools version warning that can be triggered incorrectly when custom build backends cause setuptools.__version__ to report a project’s version, and updates tests/changelog accordingly.

Changes:

• Delete _warn_on_old_setuptools() and the import-time call from the setuptools integration module.
• Remove the integration test that asserted the old warning behavior.
• Add a changelog fragment describing the fix.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
setuptools-scm/src/setuptools_scm/_integration/setuptools.py	Removes the import-time version warning logic from the setuptools integration path.
setuptools-scm/testing_scm/test_integration.py	Drops the now-obsolete warning test and related import.
setuptools-scm/changelog.d/1192.bugfix.md	Documents the warning removal and the custom build-backend false-positive scenario.

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