Fix test failures on postgres

[lukasj]

following tests are currently excluded from running on postgres

• TestQuerySyntaxFunctionTests
• TestQuerySyntaxComparisonTests
• org.eclipse.persistence.testing.tests.jpa.jpql.advanced.JUnitJPQLJakartaDataNoAliasTest
• org.eclipse.persistence.testing.tests.jpa.jpql.advanced.JUnitJPQLModifyTest

tests were disabled in #2653