fix(test): unskip gem installation tests

The gem installation tests were skipped due to a conditional bug that
tested a string literal instead of the variable. This caused the library
script to always use the PureRuby recorder and fail when running the
native gem.

Removed the skip and corrected the gem_bin check so the proper recorder
class is chosen when generating the temporary script.

Author: zah

test/test_tracer.rb

@@ -95,7 +95,6 @@ def test_args_sum_with_separator
   end
 
   def run_gem_installation_test(gem_bin, gem_module)
-    skip
     Dir.chdir(File.expand_path('..', __dir__)) do
       gem_dir = File.join('gems', gem_bin)
 
@@ -125,7 +124,7 @@ def run_gem_installation_test(gem_bin, gem_module)
         out_dir_lib = File.join('test', 'tmp', "gem_install_#{gem_bin.tr('-', '_')}_lib")
         FileUtils.rm_rf(out_dir_lib)
 
-        recorder_class = if '#{gem_bin}' == 'codetracer-ruby-recorder'
+        recorder_class = if gem_bin == 'codetracer-ruby-recorder'
           "CodeTracer::RubyRecorder"
         else
           "Codetracer::PureRubyRecorder"