Add zipcode validation for Czech republic and Slovakia

[vyskoczilova]

No description provided.

[claudiosanches]

Please, just change ( ?) to (\s?).
Thanks for your contribution.

[codecov]

Codecov Report

Merging #17956 into master will decrease coverage by <.01%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             master   #17956      +/-   ##
============================================
- Coverage      36.8%   36.79%   -<.01%     
- Complexity    12404    12406       +2     
============================================
  Files           342      342              
  Lines         46510    46514       +4     
============================================
  Hits          17114    17114              
- Misses        29396    29400       +4

Impacted Files	Coverage Δ	Complexity Δ
includes/class-wc-validation.php	5.33% <0%> (-0.3%)	24 <0> (+2)

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