fix: use the correct environment variable in watch_sass #25474

Job	Run time
lms-1(py=3.11,dj=pinned,mongo=7.0)	13m 39s
lms-2(py=3.11,dj=pinned,mongo=7.0)	13m 35s
lms-3(py=3.11,dj=pinned,mongo=7.0)	18m 53s
lms-4(py=3.11,dj=pinned,mongo=7.0)	24m 16s
lms-5(py=3.11,dj=pinned,mongo=7.0)	12m 40s
lms-6(py=3.11,dj=pinned,mongo=7.0)	19m 19s
openedx-1-with-lms(py=3.11,dj=pinned,mongo=7.0)	15m 28s
openedx-2-with-lms(py=3.11,dj=pinned,mongo=7.0)	19m 11s
openedx-1-with-cms(py=3.11,dj=pinned,mongo=7.0)	10m 16s
openedx-2-with-cms(py=3.11,dj=pinned,mongo=7.0)	7m 36s
cms-1(py=3.11,dj=pinned,mongo=7.0)	5m 9s
cms-2(py=3.11,dj=pinned,mongo=7.0)	18m 34s
common-with-lms(py=3.11,dj=pinned,mongo=7.0)	11m 50s
common-with-cms(py=3.11,dj=pinned,mongo=7.0)	6m 28s
xmodule-with-lms(py=3.11,dj=pinned,mongo=7.0)	8m 24s
xmodule-with-cms(py=3.11,dj=pinned,mongo=7.0)	8m 28s
coverage (3.11)	1m 43s
compile-warnings-report	7s
Unit tests successful	3s
	3h 35m 39s

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