fix: Request.protocol returns 'https' for HTTP/2 after RST_STREAM (#1736)

[guoyangzhen]

Fixes #1736

When using koa with http2.createSecureServer, Request.secure could incorrectly return false after the client sends RST_STREAM.

Root Cause

In HTTP/2, after a stream reset, req.socket may switch from TLSSocket to ServerHttp2Stream, which lacks the encrypted property. The protocol getter only checked this.socket.encrypted, so it fell through to 'http'.

Fix

When this.socket.encrypted is falsy, fall back to checking req.stream.session.socket.encrypted for HTTP/2 connections.

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 99.80%. Comparing base (d3ea8bf) to head (b0a07b4).

Files with missing lines	Patch %	Lines
lib/request.js	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1944      +/-   ##
==========================================
- Coverage   99.90%   99.80%   -0.10%     
==========================================
  Files           9        9              
  Lines        2094     2100       +6     
==========================================
+ Hits         2092     2096       +4     
- Misses          2        4       +2     

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