Fix: sqlpage.variables() no longer returns duplicate keys #2086

Job	Run time
docker_build (linux/arm/v7)	5m 23s
docker_build (linux/amd64)	5m 45s
docker_build (linux/arm64)	5m 47s
windows_test	3m 36s
compile_and_lint	1m 44s
test (postgres, postgres, postgres://root:Password123!@127.0.0.1/sqlpage)	1m 48s
test (odbc, postgres, Driver=PostgreSQL Unicode;Server=127.0.0.1;Port=5432;Database=sqlpage;UID=r...	2m 27s
test (mysql, mysql, mysql://root:Password123!@127.0.0.1/sqlpage)	1m 41s
test (mssql, mssql, mssql://root:Password123!@127.0.0.1/sqlpage)	1m 59s
docker_push	19s
	30m 29s

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