Rename and call unknown method tests from http2

[trivikr]

The test for unknown method in http2 was added in #883, but it was never called as the file name didn't end with .test.js
Also there was a typo in the file name unknwon-http-method.js

This code change corrects the typo in the file name, and calls it from http2.test.js

The output of the command tap test/http2/http2.test.js before the code change:

test/http2/http2.test.js ..(node:2557) ExperimentalWarning: The http2 module is an experimental API.
test/http2/http2.test.js ............................ 24/24
total ............................................... 24/24

  24 passing (393.96ms)

  ok

After the code change:

test/http2/http2.test.js ...(node:2591) ExperimentalWarning: The http2 module is an experimental API.
test/http2/http2.test.js ............................ 28/28
total ............................................... 28/28

  28 passing (414.795ms)

  ok

Checklist

• run npm run test and npm run benchmark
• commit message and code follows Code of conduct

[allevo]

LGTM

[mcollina]

LGTM

[mcollina]

Thanks!!

[github-actions]

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