fix: name return values in findEnumDiscriminator for gocritic lint

The gocritic linter flagged the unnamed return values in the
findEnumDiscriminator function. Named the return values as
fieldName and values for better documentation.

Author: lanej

gen/schema_gen.go

@@ -815,7 +815,7 @@ func (g *schemaGen) nonPrimitiveObjectEnum(name string, schema *jsonschema.Schem
 }
 
 // findEnumDiscriminator finds a string field that has unique values across all enum objects.
-func findEnumDiscriminator(objects []map[string]any) (string, []string) {
+func findEnumDiscriminator(objects []map[string]any) (fieldName string, values []string) {
 	if len(objects) == 0 {
 		return "", nil
 	}