Examples: Add #11839 repro to vue-kitchen-sink

examples/vue-kitchen-sink/src/stories/issues/11839-undefined-bolean-prop/component.vue

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+<template>
+  <div>Disabled: {{disabled}}</div>
+</template>
+
+<script>
+export default {
+  props: {
+    disabled: Boolean,
+  },
+  mounted() {
+    console.log(this.disabled); // notice this line
+  },
+};
+</script>

examples/vue-kitchen-sink/src/stories/issues/11839-undefined-bolean-prop/index.stories.js

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+import Comp from './component.vue';
+
+export default {
+  title: 'Issues/11839 undefined boolean',
+  component: Comp,
+};
+
+export const Primary = (args, { argTypes }) => {
+  return {
+    props: Object.keys(argTypes),
+    components: { Comp },
+    // template: '<Comp />', // this will log out `false`
+    template: '<Comp v-bind="$props" />', // this will log out `undefined`
+  };
+};