minor code enhancement in abstract julia codegen (#16118)

Author: wing328

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJuliaCodegen.java

@@ -67,9 +67,9 @@ public abstract class AbstractJuliaCodegen extends DefaultCodegen {
     protected Boolean exportModels;
     protected Boolean exportOperations;
 
-    protected static final DateTimeFormatter OFFSET_DATE_TIME_FORMAT = DateTimeFormatter.ISO_OFFSET_DATE_TIME;
-    protected static final SimpleDateFormat DATE_TIME_FORMAT = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSXXX", Locale.ROOT);
-    protected static final SimpleDateFormat DATE_FORMAT = new SimpleDateFormat("yyyy-MM-dd", Locale.ROOT);
+    protected final DateTimeFormatter OFFSET_DATE_TIME_FORMAT = DateTimeFormatter.ISO_OFFSET_DATE_TIME;
+    protected final SimpleDateFormat DATE_TIME_FORMAT = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSXXX", Locale.ROOT);
+    protected final SimpleDateFormat DATE_FORMAT = new SimpleDateFormat("yyyy-MM-dd", Locale.ROOT);
 
     public AbstractJuliaCodegen() {
         super();