Update tox.ini to remove Python 3.8 support #32435

Job	Run time
lms-1(py=3.11,dj=pinned,mongo=7.0)	9m 48s
lms-2(py=3.11,dj=pinned,mongo=7.0)	11m 30s
lms-3(py=3.11,dj=pinned,mongo=7.0)	16m 42s
lms-4(py=3.11,dj=pinned,mongo=7.0)	19m 51s
lms-5(py=3.11,dj=pinned,mongo=7.0)	11m 21s
collect-and-verify	4m 23s
lms-6(py=3.11,dj=pinned,mongo=7.0)	15m 14s
openedx-1-with-lms(py=3.11,dj=pinned,mongo=7.0)	10m 53s
openedx-2-with-lms(py=3.11,dj=pinned,mongo=7.0)	14m 9s
openedx-1-with-cms(py=3.11,dj=pinned,mongo=7.0)	8m 38s
openedx-2-with-cms(py=3.11,dj=pinned,mongo=7.0)	6m 27s
cms-1(py=3.11,dj=pinned,mongo=7.0)	4m 41s
cms-2(py=3.11,dj=pinned,mongo=7.0)	13m 6s
common-with-lms(py=3.11,dj=pinned,mongo=7.0)	9m 31s
common-with-cms(py=3.11,dj=pinned,mongo=7.0)	5m 35s
xmodule-with-lms(py=3.11,dj=pinned,mongo=7.0)	8m 33s
xmodule-with-cms(py=3.11,dj=pinned,mongo=7.0)	8m 34s
xmodule-with-cms(py=3.11,dj=pinned,mongo=7.0)	8m 33s
xmodule-with-lms(py=3.11,dj=pinned,mongo=7.0)	8m 43s
compile-warnings-report	9s
Unit tests successful	4s
coverage (3.11)	1m 45s
merge-artifacts	6s
	3h 18m 16s

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