Fix disabling expiration for a single request

[JWCook]

Closes #526

Looks like this was previously working in 0.8.x, but broke with #406. A test has been added to cover this.

[codecov-commenter]

Codecov Report

Merging #527 (b2ad34e) into master (04ff30b) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #527   +/-   ##
=======================================
  Coverage   98.61%   98.61%           
=======================================
  Files          18       18           
  Lines        1295     1299    +4     
  Branches      205      205           
=======================================
+ Hits         1277     1281    +4     
  Misses          9        9           
  Partials        9        9           

Impacted Files	Coverage Δ
requests_cache/cache_control.py	100.00% <100.00%> (ø)

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