Fix: Use Locator property `block_id`. #22475

Job	Run time
python-3.8,django-pinned,lms-1	10m 8s
python-3.8,django-pinned,lms-2	9m 8s
python-3.8,django-pinned,lms-3	15m 26s
python-3.8,django-pinned,lms-4	19m 9s
python-3.8,django-pinned,lms-5	9m 26s
python-3.8,django-pinned,lms-6	15m 18s
python-3.8,django-pinned,openedx-1-with-lms	12m 47s
python-3.8,django-pinned,openedx-2-with-lms	14m 25s
python-3.8,django-pinned,openedx-1-with-cms	7m 26s
python-3.8,django-pinned,openedx-2-with-cms	4m 28s
python-3.8,django-pinned,cms-1	2m 41s
python-3.8,django-pinned,cms-2	15m 14s
python-3.8,django-pinned,common-with-lms	8m 50s
python-3.8,django-pinned,common-with-cms	3m 59s
python-3.8,django-pinned,xmodule-with-lms	5m 2s
python-3.8,django-pinned,xmodule-with-cms	5m 17s
compile-warnings-report	9s
coverage (3.8)	1m 58s
Unit tests successful	4s
	2h 40m 55s

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