Update mysql2 requirement from ^3.6.5 to ^3.10.0 #511

Job	Run time
check-and-lint	27s
adapter-tests-sqlite (16.x, ubuntu-latest)	3m 35s
adapter-tests-sqlite (16.x, windows-latest)	4m 56s
adapter-tests-mysql (16.x)	9m 11s
adapter-tests-sqlite (16.x, macos-latest)	3m 18s
adapter-tests-mssql (16.x)	11m 13s
adapter-tests-mysql (18.x)	9m 17s
adapter-tests-postgres (16.x)	3m 16s
adapter-tests-sqlite (18.x, ubuntu-latest)	3m 24s
adapter-tests-mssql (18.x)	3m 17s
adapter-tests-mysql (20.x)	9m 14s
adapter-tests-postgres (18.x)	3m 21s
adapter-tests-sqlite (18.x, windows-latest)	5m 17s
adapter-tests-mssql (20.x)	3m 11s
adapter-tests-postgres (20.x)	3m 19s
adapter-tests-sqlite (18.x, macos-latest)	3m 29s
adapter-tests-sqlite (20.x, ubuntu-latest)	3m 10s
adapter-tests-sqlite (20.x, windows-latest)	6m 24s
adapter-tests-sqlite (20.x, macos-latest)	3m 25s
deploy	0s
	1h 32m 44s

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