fix(runtime-dom): avoid setting unchanged input value (#1937)

fix #1935 (fix v-model usage with HTML5 validation)

packages/runtime-dom/src/directives/vModel.ts

@@ -85,7 +85,10 @@ export const vModelText: ModelDirective<
         return
       }
     }
-    el.value = value == null ? '' : value
+    const newValue = value == null ? '' : value
+    if (el.value !== newValue) {
+      el.value = newValue
+    }
   }
 }