fix OpenStreamSync busy looping

[marten-seemann]

Fixes #2824.

[codecov]

Codecov Report

Merging #2827 into master will increase coverage by 0.58%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master    #2827      +/-   ##
==========================================
+ Coverage   85.83%   86.41%   +0.58%     
==========================================
  Files         134      134              
  Lines        9036    10375    +1339     
==========================================
+ Hits         7756     8965    +1209     
- Misses        939      978      +39     
- Partials      341      432      +91     

Impacted Files	Coverage Δ
streams_map_outgoing_generic.go	95.05% <75.00%> (-0.95%)	⬇️
stream.go	83.67% <0.00%> (-2.04%)	⬇️
qlog/qlog.go	95.09% <0.00%> (-0.29%)	⬇️
receive_stream.go	95.98% <0.00%> (-0.02%)	⬇️
internal/congestion/cubic.go	100.00% <0.00%> (ø)
internal/congestion/hybrid_slow_start.go	93.02% <0.00%> (+0.72%)	⬆️
internal/handshake/updatable_aead.go	96.98% <0.00%> (+0.74%)	⬆️
internal/congestion/cubic_sender.go	88.31% <0.00%> (+1.52%)	⬆️
send_stream.go	94.83% <0.00%> (+1.80%)	⬆️
http3/client.go	88.70% <0.00%> (+2.52%)	⬆️
... and 8 more

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[MichaelMure]

Can this be reviewed? It's affecting production for us.