Use our execute-sql! fn in metabase.test.data.sql-jdbc.load-data instead of jdbc/execute

Inside the `do-insert` method for `:sql-jdbc/test-extensions` we use jdbc's execute function but we can instead use our own execute-sql! implementation.

Start in the do-insert method for :sql-jdbc/test-extensions in metabase.test.data.sql-jdbc.load-data. Compare the current jdbc/execute call with the repository's execute-sql! implementation, then verify that the method uses execute-sql! and that the existing SQL-JDBC test data loading behavior remains unchanged.

Written by the indexing model from the issue text.