Revert "Change tests to check for Perl v5.14"

This reverts commit 27b4336 because
Dist::Zilla requires v5.20.

Author: robrwo

.github/workflows/testsuite.yml

@@ -38,7 +38,7 @@ jobs:
       - id: action
         uses: perl-actions/perl-versions@v1
         with:
-          since-perl: v5.14
+          since-perl: v5.20
           with-devel: true
 
   perl: