http: fix wrong method for /json/new

[CanadaHonk]

/json/new only accepts PUT but the docs incorrectly state to use GET. Keeps id the same so old anchor links still work.

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[paulirish]

Good call. Thanks for the report and fix.

See also discussion:

• https://chromium-review.googlesource.com/c/chromium/src/+/3595822
• https://github.com/GoogleChrome/lighthouse/pull/14063