.github/workflows: disable pkg-config on Windows tests

Let ext/openssl/extconf.rb find the correct OpenSSL installation from
the default include/library paths.

Since some time ago, the test environment contains another OpenSSL
installation and pkg-config from Mingw-w64. However, as pkg-config is
not available in RubyInstaller (Ruby 2.3), simply invoking pkg-config
command from our ext/openssl/extconf.rb ends up with picking up
Mingw-w64's OpenSSL, which is incompatible with RI.

Author: rhenium

.github/workflows/test.yml

@@ -52,10 +52,11 @@ jobs:
       - name: depends
         run:  rake install_dependencies
 
+      # pkg-config is disabled because it can pick up the different OpenSSL installation
       # SSL_DIR is set as needed by MSP-Greg/setup-ruby-pkgs
       # only used with mswin
       - name: compile
-        run:  rake compile -- --enable-debug $env:SSL_DIR
+        run:  rake compile -- --enable-debug --without-pkg-config $env:SSL_DIR
 
       - name: test
         run:  rake test TESTOPTS="-v --no-show-detail-immediately" OSSL_MDEBUG=1