`build/pkgs/python3`: Update to 3.12.4; declare support of Python 3.12.x stable #13401

Job	Run time
test-new	15m 37s
test-long (src/sage/[a-f]*)	31m 58s
test-mod (sagemath_categories-check)	10m 15s
test-long (src/sage/[g-o]*)	37m 24s
test-long (src/sage/[p-z]*)	1m 4s
test-long (src/doc src/sage_docbuild src/sage_setup)	11m 8s
coverage-report	23m 39s
	2h 11m 5s

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