fix: run DatabaseMetadata tests for PG on emulator (#2271)

* test: run DatabaseMetadata tests for PG on emulator

Run the DatabaseMetadata integration tests for PostgreSQL-dialect databases
on the emulator.

* fix: add explicit casts to function arguments

Author: olavloite

src/main/resources/com/google/cloud/spanner/jdbc/postgresql/DatabaseMetaData_GetColumns.sql

@@ -32,7 +32,7 @@ SELECT TABLE_CATALOG AS "TABLE_CAT", TABLE_SCHEMA AS "TABLE_SCHEM", TABLE_NAME A
            WHEN DATA_TYPE LIKE 'ARRAY' THEN
                CASE
                    WHEN spanner_type LIKE '%[]' THEN
-                       CONCAT('_', REPLACE(spanner_type, '[]', ''))
+                       CONCAT('_'::varchar, REPLACE(spanner_type, '[]'::varchar, ''::varchar))
                    ELSE spanner_type
                    END
            ELSE DATA_TYPE

src/test/java/com/google/cloud/spanner/jdbc/it/ITJdbcPgNumericTest.java

@@ -182,6 +182,14 @@ public void testResultSet() throws SQLException {
       assertEquals(new BigDecimal(negativeBigNumeric), resultSet.getBigDecimal("col1"));
       assertEquals(new BigDecimal(negativeBigNumeric), resultSet.getObject("col1"));
       assertEquals(Value.pgNumeric(negativeBigNumeric), resultSet.getObject("col1", Value.class));
+
+      // Just verify that the getColumns method works
+      try (ResultSet columns = connection.getMetaData().getColumns(null, null, null, null)) {
+        //noinspection StatementWithEmptyBody
+        while (columns.next()) {
+          // ignore
+        }
+      }
     }
   }