wait until the handshake is complete before updating the connection ID

[marten-seemann]

This is not required anywhere, but we don't need to unnecessarily complicate things.

[codecov]

Codecov Report

Merging #2856 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2856      +/-   ##
==========================================
+ Coverage   85.67%   85.68%   +0.01%     
==========================================
  Files         134      134              
  Lines        9087     9091       +4     
==========================================
+ Hits         7785     7789       +4     
  Misses        960      960              
  Partials      342      342              

Impacted Files	Coverage Δ
conn_id_manager.go	93.55% <100.00%> (+0.22%)	⬆️
session.go	77.27% <100.00%> (+0.02%)	⬆️

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