Include PHP 7.4 and 7.3 in test matrix

[ocean90]

Description Fixes #175

How has this been tested?

Screenshots If applicable, add screenshots to show the visual change.

Types of changes

Checklist:

• [ ] My code is tested.
• [ ] My code follows the WordPress code style.
• [ ] My code has proper inline documentation.

[codecov[bot]]

Codecov Report

Merging #179 into master will decrease coverage by 79.63%. The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master    #179       +/-   ##
============================================
- Coverage     79.63%   0.00%   -79.64%     
+ Complexity      397      65      -332     
============================================
  Files            24       2       -22     
  Lines           928     238      -690     
============================================
- Hits            739       0      -739     
- Misses          189     238       +49     

Impacted Files	Coverage Δ	Complexity Δ
inc/Plugin.php	0.00% <0.00%> (-41.77%)	40.00 <2.00> (-31.00)
inc/ZipProvider.php	0.00% <0.00%> (-98.83%)	25.00 <22.00> (ø)

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