Update HandlebarsEngineAdapter.java

The old MY_FIELD_VALUE_RESOLVER.INSTANCE is equivalent to FieldValueResolver.INSTANCE, which is assigned `new FieldValueResolver();` so our custom class was never used.

modules/openapi-generator/src/main/java/org/openapitools/codegen/templating/HandlebarsEngineAdapter.java

@@ -74,7 +74,7 @@ public TemplateSource sourceAt(String location) {
         };
 
         // $ref: https://github.com/jknack/handlebars.java/issues/917
-        var MY_FIELD_VALUE_RESOLVER = new FieldValueResolver() {
+        var accessAwareFieldValueResolverInstance = new FieldValueResolver() {
             @Override
             protected Set<FieldWrapper> members(
                     Class<?> clazz) {
@@ -101,7 +101,7 @@ boolean isValidField(
                 .resolver(
                         MapValueResolver.INSTANCE,
                         JavaBeanValueResolver.INSTANCE,
-                        MY_FIELD_VALUE_RESOLVER.INSTANCE,
+                        accessAwareFieldValueResolverInstance,
                         MethodValueResolver.INSTANCE)
                 .build();