Animation of new elements

[shengxinjing]

Describe the bug

If you use css animation for new elements, the animation will be rendered twice.

Reproduction

https://github.com/shengxinjing/vue-virtual-scroller/commit/13fafd8487d603fb597cb844b747ca0885feb886

System Info

System:
    OS: macOS 13.4.1
    CPU: (10) arm64 Apple M1 Max
    Memory: 2.27 GB / 64.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 18.12.0 - /usr/local/bin/node
    Yarn: 1.22.7 - ~/node_modules/.bin/yarn
    npm: 8.19.2 - /usr/local/bin/npm
    pnpm: 8.6.5 - ~/Library/pnpm/pnpm
    bun: 1.0.0 - /usr/local/bin/bun
  Browsers:
    Chrome: 120.0.6099.129
    Safari: 16.5.2

Used Package Manager

pnpm

Validations

• [X] Read the docs.
• [X] Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• [X] Check that this is a concrete bug. For Q&A open a GitHub Discussion.
• [X] The provided reproduction is a minimal reproducible example of the bug.