fix: fix breadcrumb separator

[flyerH]

[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
• Refactoring
• Code style optimization
• Test Case
• Branch merge
• Other (about what?)

🔗 Related issue link

close #25975

💡 Background and solution

Add a default separator for BreadcrumbItem.

📝 Changelog

Language	Changelog
🇺🇸 English	Fix Breadcrumb.Item lost separator after wrapping in component.
🇨🇳 Chinese	修复 Breadcrumb.Item 封装后丢失分隔符的问题。

☑️ 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

[ant-design-bot]

[ant-design-bot]

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit 11bb2ff:

Sandbox	Source
antd reproduction template	Configuration
flamboyant-faraday-tp9fg	Issue #25975

[MrHeer]

Your PR has only one commit and it's not semantic.

[flyerH]

Your PR has only one commit and it's not semantic.

updated 😁

[codecov]

Codecov Report

Merging #25984 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master   #25984   +/-   ##
=======================================
  Coverage   99.57%   99.57%           
=======================================
  Files         373      373           
  Lines        7313     7314    +1     
  Branches     2041     1994   -47     
=======================================
+ Hits         7282     7283    +1     
  Misses         31       31           

Impacted Files	Coverage Δ
components/breadcrumb/BreadcrumbItem.tsx	100.00% <100.00%> (ø)

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[afc163]

Could you add a test case?