build: Cache images in unit tests #33120

Job	Run time
collect-and-verify	3m 7s
lms-1(py=3.11,dj=pinned,mongo=7.0)	8m 40s
lms-2(py=3.11,dj=pinned,mongo=7.0)	10m 35s
lms-3(py=3.11,dj=pinned,mongo=7.0)	14m 34s
lms-4(py=3.11,dj=pinned,mongo=7.0)	18m 55s
lms-5(py=3.11,dj=pinned,mongo=7.0)	9m 57s
lms-6(py=3.11,dj=pinned,mongo=7.0)	15m 57s
openedx-1-with-lms(py=3.11,dj=pinned,mongo=7.0)	10m 1s
openedx-2-with-lms(py=3.11,dj=pinned,mongo=7.0)	13m 23s
openedx-1-with-cms(py=3.11,dj=pinned,mongo=7.0)	7m 25s
openedx-2-with-cms(py=3.11,dj=pinned,mongo=7.0)	5m 21s
cms-1(py=3.11,dj=pinned,mongo=7.0)	3m 36s
cms-2(py=3.11,dj=pinned,mongo=7.0)	11m 30s
common-with-lms(py=3.11,dj=pinned,mongo=7.0)	8m 35s
common-with-cms(py=3.11,dj=pinned,mongo=7.0)	4m 37s
xmodule-with-lms(py=3.11,dj=pinned,mongo=7.0)	7m 18s
xmodule-with-cms(py=3.11,dj=pinned,mongo=7.0)	7m 32s
xmodule-with-cms(py=3.11,dj=pinned,mongo=7.0)	8m 6s
xmodule-with-lms(py=3.11,dj=pinned,mongo=7.0)	7m 45s
compile-warnings-report	12s
Unit tests successful	2s
coverage (3.11)	1m 35s
merge-artifacts	7s
	2h 58m 50s

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