[ruby/rubygems] Move bundler test tmp directory from bundler/tmp to top-level tmp

The bundler tests were writing temporary files to bundler/tmp, but this
moves them to the repository's top-level tmp directory instead, which is
already covered by .gitignore. All references in CI workflows, SimpleCov
filters, rubocop excludes, codespell config, and documentation have been
updated accordingly.

ruby/rubygems@89f4def64a

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 2 people

spec/bundler/spec_helper.rb

@@ -56,7 +56,7 @@
     add_filter "/lib/rubygems/"
     add_filter "/lib/bundler/vendor/"
     add_filter "/tool/"
-    add_filter "/bundler/tmp/"
+    add_filter "/tmp/"
     add_filter ".gemspec"
   end
 

spec/bundler/support/path.rb

@@ -123,7 +123,7 @@ def tmp_root
         end
         Pathname(real)
       else
-        source_root.join("tmp")
+        Pathname.new("../..").expand_path(__dir__).join("tmp")
       end
     end