test(h2): cover stream reset with NGHTTP2_INTERNAL_ERROR

[zeexzeex]

A stream reset before the response headers arrive settles the request promise
with ERR_HTTP2_STREAM_ERROR, carrying the reset code in http2ErrorCode.
That is a different path from a plain stream.close(), which surfaces an
InformationalError:

server sends	code	http2ErrorCode
stream.close()	UND_ERR_INFO	–
stream.close(INTERNAL_ERROR)	ERR_HTTP2_STREAM_ERROR	2
stream.close(CANCEL)	UND_ERR_INFO	–

test/http2-destroy-after-failed-stream.js covers the first row, and the only
existing use of NGHTTP2_INTERNAL_ERROR in the test suite is a session-level
goaway(). The stream-level reset path is currently untested.

Changes

Adds two tests:

• a request whose stream is reset with NGHTTP2_INTERNAL_ERROR rejects with
  the expected code and http2ErrorCode
• the failed stream does not prevent other requests on the same connection
  from completing

No production code is changed; this only pins down existing behaviour.

I verified the tests actually catch a regression by removing the
state.abort(err) call in onError (reproducing the behaviour reported in
#2675) and confirming both tests fail, then restoring it.

Refs: #2675

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.46%. Comparing base (fc3450d) to head (ce3aa44).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5725      +/-   ##
==========================================
- Coverage   93.47%   93.46%   -0.01%     
==========================================
  Files         110      110              
  Lines       38908    38908              
==========================================
- Hits        36368    36366       -2     
- Misses       2540     2542       +2     

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