fix(fetch): remove incomplete sentence

[avivkeller]

Description

This PR removes the incomplete sentence in the fetch learn guide, and instead references the "Specification Compliance" section of the official Undici documentation.

Related Issues

Fixes #7568

Check List

• I have read the Contributing Guidelines and made commit messages that follow the guideline.
• I have run npm run format to ensure the code follows the style guide.
• I have run npm run test to check if all tests are passing.
• I have run npx turbo build to check if the website builds without errors.
• I've covered new added functionality with unit tests if necessary.

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Name	Status	Preview	Updated (UTC)
nodejs-org	✅ Ready (Inspect)	Visit Preview	Apr 17, 2025 9:02pm

[Copilot]

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

[github-actions]

Lighthouse Results

URL	Performance	Accessibility	Best Practices	SEO	Report
/en	🟢 99	🟢 100	🟢 100	🟢 91	🔗
/en/about	🟢 100	🟢 100	🟢 100	🟢 91	🔗
/en/about/previous-releases	🟢 99	🟢 100	🟢 100	🟢 92	🔗
/en/download	🟢 98	🟢 100	🟢 100	🟢 91	🔗
/en/blog	🟢 100	🟢 100	🟢 96	🟢 92	🔗

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.63%. Comparing base (c0d6b17) to head (8309f49).
Report is 1 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7654      +/-   ##
==========================================
+ Coverage   74.61%   74.63%   +0.02%     
==========================================
  Files          96       96              
  Lines        7685     7685              
  Branches      192      192              
==========================================
+ Hits         5734     5736       +2     
+ Misses       1949     1947       -2     
  Partials        2        2              

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