fix: BackTop should disappear when fade out

[afc163]

[中文版模板 / Chinese template]

🤔 This is a ...

• New feature
• Bug fix
• Site / documentation update
• Demo update
• Component style update
• TypeScript definition update
• Bundle size optimization
• Performance optimization
• Enhancement feature
• Internationalization
• Refactoring
• Code style optimization
• Test Case
• Branch merge
• Other (about what?)

🔗 Related issue link

close #31253

💡 Background and solution

📝 Changelog

Language	Changelog
🇺🇸 English	Fix BackTop not disappear when fade out.
🇨🇳 Chinese	修复 BackTop 隐出后仍然可以交互的问题。

☑️ Self Check before Merge

⚠️ Please check all items below before review. ⚠️

• 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

[github-actions]

[github-actions]

Size Change: -46 B (0%)

Total Size: 832 kB

Filename	Size	Change
./dist/antd-with-locales.min.js	341 kB	-23 B (0%)
./dist/antd.min.js	297 kB	-23 B (0%)

ℹ️ View Unchanged

Filename	Size
./dist/antd.compact.min.css	64.3 kB
./dist/antd.dark.min.css	65.6 kB
./dist/antd.min.css	64.4 kB

_{compressed-size-action}

[codecov]

Codecov Report

Merging #31357 (663df2a) into master (8022019) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master    #31357   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          397       397           
  Lines         7570      7567    -3     
  Branches      2134      2134           
=========================================
- Hits          7570      7567    -3     

Impacted Files	Coverage Δ
components/form/ErrorList.tsx	100.00% <ø> (ø)
components/back-top/index.tsx	100.00% <100.00%> (ø)

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