fix LinkCheckCreatedAt set to None #33151

Job	Run time
collect-and-verify	2m 58s
lms-1(py=3.11,dj=pinned,mongo=7.0)	8m 31s
lms-2(py=3.11,dj=pinned,mongo=7.0)	10m 26s
lms-3(py=3.11,dj=pinned,mongo=7.0)	11m 58s
lms-4(py=3.11,dj=pinned,mongo=7.0)	11m 58s
lms-5(py=3.11,dj=pinned,mongo=7.0)	9m 46s
lms-6(py=3.11,dj=pinned,mongo=7.0)	11m 56s
openedx-1-with-lms(py=3.11,dj=pinned,mongo=7.0)	10m 20s
openedx-2-with-lms(py=3.11,dj=pinned,mongo=7.0)	11m 57s
openedx-1-with-cms(py=3.11,dj=pinned,mongo=7.0)	6m 57s
openedx-2-with-cms(py=3.11,dj=pinned,mongo=7.0)	5m 7s
cms-1(py=3.11,dj=pinned,mongo=7.0)	3m 34s
cms-2(py=3.11,dj=pinned,mongo=7.0)	11m 43s
common-with-lms(py=3.11,dj=pinned,mongo=7.0)	7m 46s
common-with-cms(py=3.11,dj=pinned,mongo=7.0)	4m 11s
xmodule-with-lms(py=3.11,dj=pinned,mongo=7.0)	7m 16s
xmodule-with-cms(py=3.11,dj=pinned,mongo=7.0)	7m 14s
xmodule-with-cms(py=3.11,dj=pinned,mongo=7.0)	8m 3s
xmodule-with-lms(py=3.11,dj=pinned,mongo=7.0)	7m 42s
Unit tests successful	1s
coverage	0s
compile-warnings-report	0s
merge-artifacts	0s
	2h 39m 24s

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