Auto merge of #13733 - jeenalee:request-clone, r=jdm

Fix Request's Headers to be cloned correctly

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Previously, when `Clone()` was called, Headers of the template Request did not get cloned properly. This commit fixes that issue, and updates the expected wpt results.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #11894 (github issue number if applicable).

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- [ ] These changes do not require tests because _____

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