[Perl/perl5] 7c1600: testsuite.yml: manually download and extract mingw

[xenu via perl5-changes]

  Branch: refs/heads/blead
  Home:   https://github.com/Perl/perl5
  Commit: 7c1600f08167a99af2b98ebb9b3230080a59d563
      
https://github.com/Perl/perl5/commit/7c1600f08167a99af2b98ebb9b3230080a59d563
  Author: Tomasz Konojacki <m...@xenu.pl>
  Date:   2023-07-18 (Tue, 18 Jul 2023)

  Changed paths:
    M .github/workflows/testsuite.yml

  Log Message:
  -----------
  testsuite.yml: manually download and extract mingw

This is much faster than the "setup-mingw" GitHub action (~1 min vs
~6min). It's also more flexible, we can easily switch to a different
mingw build.