Attributes with `undefined` value are not removed

[Gwynerva]

Vue version

5.8.3

Link to minimal reproduction

Playground

Steps to reproduce

<script lang="ts" setup>
import { ref } from 'vue'

const msg = ref('Hello World!')
</script>

<template>
  <h1 :style="undefined" :class="undefined">{{ msg }}</h1>
  <input v-model="msg" />
</template>

When SSR is OFF it renders <h1 class>...</h1>.
When SSR is ON it renders <h1 style class>...</h1>.

What is expected?

When attribute has undefined value it should be completely removed from node: <h1>...</h1>

What is actually happening?

Attribute names are present but with empty values.

[jacekkarczmarczyk]

#3173