use the KEY_UPDATE_ERROR

[marten-seemann]

Fixes #2767.

[codecov]

Codecov Report

Merging #2770 into master will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2770      +/-   ##
==========================================
+ Coverage   86.67%   86.73%   +0.06%     
==========================================
  Files         128      128              
  Lines       10001    10023      +22     
==========================================
+ Hits         8668     8693      +25     
+ Misses       1006     1004       -2     
+ Partials      327      326       -1     

Impacted Files	Coverage Δ
internal/handshake/updatable_aead.go	97.06% <100.00%> (ø)
internal/qerr/error_codes.go	100.00% <100.00%> (ø)
qlog/types.go	84.98% <100.00%> (+0.14%)	⬆️
http3/request.go	98.41% <0.00%> (+7.30%)	⬆️

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