disable key updates when using HTTP/3 to avoid breaking Chrome 87

[marten-seemann]

Fixes #2901.

[codecov]

Codecov Report

Merging #2906 (35690c5) into master (a76879c) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2906   +/-   ##
=======================================
  Coverage   85.77%   85.77%           
=======================================
  Files         133      133           
  Lines        9180     9181    +1     
=======================================
+ Hits         7874     7875    +1     
  Misses        958      958           
  Partials      348      348           

Impacted Files	Coverage Δ
http3/server.go	65.16% <100.00%> (+0.16%)	⬆️

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[mvdan]

SGTM. Do we want a TODO to remember to remove this at some point later, once Chrome 87 is no longer supported/used anymore?

[marten-seemann]

@mvdan Opened a new issue instead: #2926.