Fix missing gem spec test

Our test for skipping RBI for missing gem specs was broken by a change
in how bundler represents specs for default gems
(rubygems/rubygems#7673), and thus changes
when they're considered "missing." Our test happened to use a default
gem, which is why it broke. However, the test doesn't rely on
the example being a default gem, so we can change it to a different
gem, which will fix the test.

spec/tapioca/cli/gem_spec.rb

@@ -706,16 +706,16 @@ class Secret; end
         it "must not generate RBIs for missing gem specs" do
           @project.write_gemfile!(<<~GEMFILE, append: true)
             platform :rbx do
-              gem "ruby2_keywords", "0.0.5"
+              gem "psych", "=5.1.2"
             end
           GEMFILE
 
           @project.bundle_install!
 
           result = @project.tapioca("gem --all")
 
-          assert_stdout_includes(result, "completed with missing specs: ruby2_keywords (0.0.5)")
-          refute_includes(result.out, "Compiled ruby2_keywords")
+          assert_stdout_includes(result, "completed with missing specs: psych (5.1.2)")
+          refute_includes(result.out, "Compiled psych")
 
           assert_empty_stderr(result)
           assert_success_status(result)