chore: remove mysql57 #709

Job	Run time
run_ci (ubuntu-20.04, 3.11, discovery+lms+forum)	22m 12s
run_ci (ubuntu-20.04, 3.11, registrar+lms)	16m 25s
run_ci (ubuntu-20.04, 3.11, ecommerce+lms)	21m 41s
run_ci (ubuntu-20.04, 3.11, edx_notes_api+lms)	15m 39s
run_ci (ubuntu-20.04, 3.11, credentials+lms)	18m 44s
run_ci (ubuntu-20.04, 3.11, xqueue)	3m 51s
run_ci (ubuntu-20.04, 3.11, analyticsapi+insights+lms)	22m 16s
run_ci (ubuntu-20.04, 3.11, designer+lms)	17m 6s
run_ci (ubuntu-20.04, 3.11, enterprise-subsidy+enterprise-catalog+enterprise-access+lms)	24m 39s
run_ci (ubuntu-20.04, 3.11, license-manager+lms)	17m 11s
	2h 59m 44s

Provide feedback