Add a CI test for basic rubygems functionality without openssl

The whole test suite actually passes on my system, but it has weird
errors in CI. Since I don't want to spend time on it, instead of running
the whole test suite, I'm just adding a bare test to check that `gem
list` works.

.github/workflows/install-rubygems.yml

@@ -14,6 +14,7 @@ jobs:
     strategy:
       matrix:
         ruby: [ 2.3.8, 2.4.10, 2.5.8, 2.6.6, 2.7.1, jruby-9.2.11.1 ]
+        openssl: [true, false]
     steps:
       - uses: actions/checkout@v2
       - name: Setup ruby
@@ -25,6 +26,11 @@ jobs:
         run: ruby -Ilib -S rake install 2> errors.txt
       - name: Check rubygems install produced no warnings
         run: test ! -s errors.txt || (cat errors.txt && exit 1)
+      - name: Simulate no openssl
+        run: ruby util/remove_openssl.rb
+        if: matrix.openssl == false
+      - name: Run installed rubygems
+        run: gem list bundler
       - name: Run bundler installed as a default gem
         run: bundle --version
       - name: Check bundler man pages were installed and are properly picked up

util/remove_openssl.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require "rbconfig"
+require "fileutils"
+
+archdir = RbConfig::CONFIG["archdir"]
+rubylibdir = RbConfig::CONFIG["rubylibdir"]
+default_specifications_dir = Gem.default_specifications_dir
+
+openssl_rb = File.join(rubylibdir, "openssl.rb")
+openssl_gemspec = Dir.glob("#{default_specifications_dir}/openssl-*.gemspec").first
+
+openssl_ext = if RUBY_PLATFORM == "java"
+                File.join(rubylibdir, "jopenssl.jar")
+              else
+                File.join(archdir, "openssl.so")
+              end
+
+FileUtils.mv openssl_rb, openssl_rb + "_"
+FileUtils.mv openssl_ext, openssl_ext + "_"
+FileUtils.mv openssl_gemspec, openssl_gemspec + "_" if openssl_gemspec