Honor PEP 621 `requires-python` setting. #4948

Job	Run time
Check towncrier / Towncrier Checks	23s
Package Automation / Create Python Package	24s
Package Briefcase / Create Python Package	29s
Pre-commit checks / Pre-commit Checks	1m 3s
Unit tests (macos-12, 3.9)	53s
Unit tests (macos-12, 3.12)	2m 25s
Unit tests (macos-12, 3.13-dev)	3m 1s
Unit tests (macos-14, 3.9)	39s
Unit tests (macos-14, 3.12)	1m 16s
Unit tests (macos-14, 3.13-dev)	1m 25s
Unit tests (windows-latest, 3.9)	1m 14s
Unit tests (windows-latest, 3.12)	3m 17s
Unit tests (windows-latest, 3.13-dev)	3m 53s
Unit tests (ubuntu-latest, 3.9)	38s
Unit tests (ubuntu-latest, 3.12)	1m 54s
Unit tests (ubuntu-latest, 3.13-dev)	2m 3s
Unit tests (ubuntu-latest, 3.10, false)	1m 32s
Unit tests (ubuntu-latest, 3.11, false)	1m 32s
Project coverage	49s
Verify project	0s
Build app	0s
	28m 50s

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