feat: allow h2 pseudo-header

[tsctx]

Needed for #2410

This relates to...

Fixes #2415

Rationale

See #2415

Changes

TODO

Features

N/A

Bug Fixes

N/A

Breaking Changes and Deprecations

N/A

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

[codecov-commenter]

Codecov Report

Attention: 31 lines in your changes are missing coverage. Please review.

Comparison is base (e39a632) 85.54% compared to head (0c9c7dd) 85.71%.
Report is 83 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2417      +/-   ##
==========================================
+ Coverage   85.54%   85.71%   +0.16%     
==========================================
  Files          76       76              
  Lines        6858     6937      +79     
==========================================
+ Hits         5867     5946      +79     
  Misses        991      991              

Files	Coverage Δ
index-fetch.js	100.00% <100.00%> (ø)
lib/api/api-stream.js	100.00% <100.00%> (ø)
lib/core/connect.js	80.00% <100.00%> (-1.25%)	⬇️
lib/fetch/body.js	97.68% <100.00%> (ø)
lib/fetch/constants.js	97.22% <100.00%> (+0.67%)	⬆️
lib/fetch/file.js	94.31% <100.00%> (-1.09%)	⬇️
lib/fetch/global.js	100.00% <ø> (ø)
lib/fetch/response.js	97.04% <100.00%> (+1.20%)	⬆️
lib/fetch/util.js	86.20% <100.00%> (+0.38%)	⬆️
lib/fetch/webidl.js	94.50% <100.00%> (-0.03%)	⬇️
... and 10 more

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