fix the type holder, still doesn't resolve the issue

Author: schauder

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/core/convert/MappingJdbcConverterUnitTests.java

@@ -75,6 +75,9 @@ class MappingJdbcConverterUnitTests {
 			new JdbcCustomConversions(List.of(CustomIdToLong.INSTANCE)), //
 			typeFactory //
 	);
+	{
+		context.setSimpleTypeHolder(converter.getConversions().getSimpleTypeHolder());
+	}
 
 	@Test
 		// DATAJDBC-104, DATAJDBC-1384