Merge branch 'yd/use-test-config-unconfig'

Bulk-update of the test suite. * yd/use-test-config-unconfig: t5520: use test_config to set/unset git config variables (leftover bits) t7600: use test_config to set/unset git config variables t7502: remove clear_config t7502: use test_config to set/unset git config variables t9500: use test_config to set/unset git config variables t7508: use test_config to set/unset git config variables t7500: use test_config to set/unset git config variables t5541: use test_config to set/unset git config variables t5520: use test_config to set/unset git config variables t4202: use test_config/test_unconfig to set/unset git config variables t4034: use test_config/test_unconfig to set/unset git config variables t4304: use test_config to set/unset git config variables t3400: use test_config to set/unset git config variables