fix(typescript): add Date instance check before date formatting (#21722)

* fix(typescript): add Date instance check before date formatting

* chore(typescript): generate samples

* fix: resolve type errors in ObjectSerializer Date formatting

* chore: update samples

* chore: ensure-up-to-date

Author: 0x5457

modules/openapi-generator/src/main/resources/typescript/model/ObjectSerializer.mustache

@@ -177,13 +177,16 @@ export class ObjectSerializer {
             }
             return transformedData;
         } else if (type === "Date") {
+            if (!(data instanceof Date)) {
+                return data;
+            }
             if (format == "date") {
                 let month = data.getMonth()+1
-                month = month < 10 ? "0" + month.toString() : month.toString()
+                let monthStr = month < 10 ? "0" + month.toString() : month.toString()
                 let day = data.getDate();
-                day = day < 10 ? "0" + day.toString() : day.toString();
+                let dayStr = day < 10 ? "0" + day.toString() : day.toString();
 
-                return data.getFullYear() + "-" + month + "-" + day;
+                return data.getFullYear() + "-" + monthStr + "-" + dayStr;
             } else {
                 return data.toISOString();
             }