fix(ssr): fix hydration mismatch warning about mutiple continuous tex…

[zhangzhonghe]

…t vnodes (#7285)

fix #7285

The following Comp will be rendered as a "<div>foo</div>" on the ssr side.

const Comp = defineComponent(() => h('div', ['fo', 'o']))

The "<div>foo</div>" will be rendered as a div element with a single child text node in the browser, but the above Comp will be rendered by Vue as a div element with two child vnodes, so will cause a mismatch warning during hydration.