fix: fixup theming setup during devstack provisioning #660

Job	Run time
run_ci (ubuntu-20.04, 3.11, discovery+lms+forum)	22m 29s
run_ci (ubuntu-20.04, 3.11, registrar+lms)	17m 3s
run_ci (ubuntu-20.04, 3.11, ecommerce+lms)	21m 26s
run_ci (ubuntu-20.04, 3.11, edx_notes_api+lms)	16m 33s
run_ci (ubuntu-20.04, 3.11, credentials+lms)	18m 2s
run_ci (ubuntu-20.04, 3.11, xqueue)	3m 8s
run_ci (ubuntu-20.04, 3.11, analyticsapi+insights+lms)	22m 30s
run_ci (ubuntu-20.04, 3.11, designer+lms)	17m 22s
run_ci (ubuntu-20.04, 3.11, enterprise-catalog+enterprise-access+lms)	22m 59s
run_ci (ubuntu-20.04, 3.11, license-manager+lms)	17m 48s
	2h 59m 20s

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