improve tests

.gitlab-ci.yml

lib/auth/credentials/scram.go

...lers/discovery/discoverers/google_cloud_sql/discoverer.go

lib/gat/handlers/pgbouncer/module.go

lib/gsql/query_test.go

lib/gsql/row.go

lib/rob/schedulers/v3/scheduler.go

lib/rob/schedulers/v3/scheduler_test.go

lib/util/mio/listener.go

lib/util/mio/readwritecloser.go

lib/util/rbtree/rbtree_test.go

test/inst/bind.go

test/inst/close.go

test/inst/copydata.go

test/inst/copydone.go

test/inst/describe.go

test/inst/execute.go

test/inst/instruction.go

test/inst/parse.go

test/inst/simplequery.go