Fix cookies not being sent by classic Dispatcher.

[markstory]

Cookies are not arrays anymore. We lacked test coverage for this in the past.

Refs #11070

[codecov-io]

Codecov Report

Merging #11097 into master will increase coverage by 0.08%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master   #11097      +/-   ##
============================================
+ Coverage     94.86%   94.94%   +0.08%     
- Complexity    12838    13059     +221     
============================================
  Files           437      437              
  Lines         32733    33061     +328     
============================================
+ Hits          31051    31389     +338     
+ Misses         1682     1672      -10

Impacted Files	Coverage Δ	Complexity Δ
src/Http/Response.php	93.63% <100%> (+1.04%)	257 <0> (ø)	⬇️
src/Http/ActionDispatcher.php	100% <0%> (ø)	21% <0%> (+2%)	⬆️
src/Controller/Controller.php	99.53% <0%> (+0.07%)	102% <0%> (+25%)	⬆️
src/Http/ServerRequest.php	99.65% <0%> (+0.16%)	432% <0%> (+194%)	⬆️
src/Cache/Engine/FileEngine.php	90.05% <0%> (+1.1%)	73% <0%> (ø)	⬇️
src/Cache/CacheRegistry.php	100% <0%> (+4%)	11% <0%> (ø)	⬇️

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