add more exhaustive tests for sqlpage.variables #2085

Job	Run time
docker_build (linux/arm64)	5m 47s
compile_and_lint	1m 44s
docker_build (linux/arm/v7)	5m 22s
test (odbc, postgres, Driver=PostgreSQL Unicode;Server=127.0.0.1;Port=5432;Database=sqlpage;UID=r...	2m 8s
test (postgres, postgres, postgres://root:Password123!@127.0.0.1/sqlpage)	1m 49s
windows_test	2m 54s
test (mysql, mysql, mysql://root:Password123!@127.0.0.1/sqlpage)	1m 31s
test (mssql, mssql, mssql://root:Password123!@127.0.0.1/sqlpage)	1m 42s
docker_build (linux/amd64)	5m 18s
docker_push	14s
	28m 29s

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