chore(deps): update actions/setup-python action to v6.3.0 #3375

Job	Run time
Integration Tests (pdm.lock)	32s
test (3.12, ubuntu-latest)	51s
test (3.12, windows-latest)	1m 17s
test (3.13, ubuntu-latest)	42s
test_min_deps (windows-latest)	1m 51s
test (3.12, macos-latest)	1m 57s
test (3.14, windows-latest)	1m 33s
test (3.14, ubuntu-latest)	42s
test_min_deps (macos-latest)	32s
Integration Tests (pdm.minimal.lock)	33s
test (3.14, macos-latest)	40s
test (3.13, windows-latest)	1m 29s
test (3.13, macos-latest)	32s
test (3.11, ubuntu-latest)	44s
test (3.11, macos-latest)	35s
test (3.11, windows-latest)	1m 15s
test_min_deps (ubuntu-latest)	34s
Combine & check coverage	10s
	16m 29s

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