fix: Move table-bg less variable into table background instead of td

[zombieJ]

🤔 This is a ...

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

🔗 Related issue link

fix #20756

💡 Background and solution

Since we already provides @table-bg background color. Maybe not good to make it as transparent. Move into table bg instead.

📝 Changelog

Language	Changelog
🇺🇸 English	Fix Table background color css priority to high to override user customize style.
🇨🇳 Chinese

☑️ 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

[netlify]

Deploy preview for ant-design ready!

Built with commit 9e87bf8

https://deploy-preview-20794--ant-design.netlify.com

[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 9e87bf8:

Sandbox	Source
antd reproduction template	Configuration

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@935a984). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master   #20794   +/-   ##
=========================================
  Coverage          ?   97.47%           
=========================================
  Files             ?      296           
  Lines             ?     6878           
  Branches          ?     1911           
=========================================
  Hits              ?     6704           
  Misses            ?      174           
  Partials          ?        0

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 935a984...9e87bf8. Read the comment docs.