bug(material/tabs): tab body height animation is broken

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

You can even see this behaviour in the tab example in the docs https://material.angular.dev/components/tabs/examples
scroll down to the "Tab group that keeps its content inside the DOM when it's off-screen." example
it instantly hides the first tab content when u click the second, instead of waiting for the animation to complete, leading to a glitchy stutter

### Reproduction

look at angular material's own docs ^

### Expected Behavior

it should keep the content showing until the animation is completely done

### Actual Behavior

it glitches and hides instantly

### Environment

- Angular:
- CDK/Material:
- Browser(s):
- Operating System (e.g. Windows, macOS, Ubuntu):

Angular Material のドキュメントにある「Tab group that keeps its content inside the DOM when it's off-screen」の例で問題を再現してください。まず、タブを切り替えたときのタブ本体の高さのアニメーションと、コンテンツの表示状態の挙動を追跡します。前のタブのコンテンツがアニメーションの完了まで表示されたままになり、報告されているカクつきが発生しなければ完了です。

索引モデルが issue の本文から書いたものです。