Fix list item style

[afc163]

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[中文版模板 / Chinese template]

🤔 This is a ...

• New feature
• Bug fix
• Site / document update
• Component style update
• TypeScript definition update
• Refactoring
• Code style optimization
• Branch merge
• Other (about what?)

👻 What's the background?

1. Describe the source of requirement, like related issue link.

close #15329

2. Describe the problem and the scenario.

horizonal List should align center

version	codesandbox	good or bad
3.14.1	https://codesandbox.io/s/q3qykjl40q	✅
3.15.0	https://codesandbox.io/s/vq4zokpz8l	❌

horizontal List should show extra in right edge

version	codesandbox	good or bad
3.14.1	https://codesandbox.io/s/61pl82lwvk	❌
3.15.0	https://codesandbox.io/s/z36m1693nx	❌

horizontal List should be flex container when no string nodes

version	codesandbox	good or bad
3.14.1	https://codesandbox.io/s/lz1lq824l	❌
3.15.0	https://codesandbox.io/s/znoq759zmx	✅

vertical List should always be flex container

version	codesandbox	good or bad
3.14.1	https://codesandbox.io/s/m9qx42l6kj	✅
3.15.0	https://codesandbox.io/s/848r52kk50	❌

📝 Changelog description

Describe changes from user side, and list all potential break changes or other risks.

1. English description

• Fix some List Item styling issues. 🐛 List style problem in 3.15.0 #15329

2. Chinese description (optional)

☑️ Self Check before Merge

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• TypeScript definition is updated/provided or not needed
• Changelog is provided or not needed

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[codecov]

Codecov Report

Merging #15328 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #15328      +/-   ##
==========================================
+ Coverage    94.1%   94.11%   +<.01%     
==========================================
  Files         250      250              
  Lines        6637     6643       +6     
  Branches     1906     1907       +1     
==========================================
+ Hits         6246     6252       +6     
  Misses        390      390              
  Partials        1        1

Impacted Files	Coverage Δ
components/list/index.tsx	97.26% <ø> (ø)	⬆️
components/list/Item.tsx	100% <100%> (ø)	⬆️

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