Fix flaky spec failuretests/fix_another_potential_flaky

If our test code happens to run `Gem.configuration` before `ENV["HOME"]`
is changed for our tests, this test starts failing because the test
first writes to the global `~/.gemrc` file (not in `tmp/`), because
`Gem.config_file` has that value memoized. Then, however, the `bundle
install` subprocess infers `Gem.config_file` from the modified
`ENV["HOME"]` and tries to read `tmp/home/.gemrc`. However, that file
doesn't exist, so rubygems configuration is ignored and doesn't print an
error like the test expects.

The error looks like this:

```
Failures:

  1) Bundler friendly errors with invalid YAML in .gemrc reports a relevant friendly error message
     Failure/Error: expect(err).to include("Failed to load #{home(".gemrc")}")

       expected "" to include "Failed to load /home/travis/build/rubygems/bundler/tmp/1/home/.gemrc"

       Commands:
       $  /home/travis/.rvm/rubies/ruby-2.6.5/bin/ruby -I/home/travis/build/rubygems/bundler/lib:/home/travis/build/rubygems/bundler/spec -rsupport/hax -rsupport/artifice/fail /home/travis/build/rubygems/bundler/exe/bundle install
       Running `bundle install` with bundler 3.0.0
       Found changes from the lockfile, re-resolving dependencies because the list of sources changed, the dependencies in your gemfile changed, you added a new platform to your gemfile
       Fetching source index from file:///home/travis/build/rubygems/bundler/tmp/1/gems/remote1/
       Resolving dependencies...
       Using bundler 3.0.0
       0:  bundler (3.0.0) from /home/travis/build/rubygems/bundler/lib/bundler/source
       Fetching rack 1.0.0
       Installing rack 1.0.0
       Rack's post install message
       0:  rack (1.0.0) from /home/travis/build/rubygems/bundler/tmp/1/bundled_app/.bundle/ruby/2.6.0/specifications/rack-1.0.0.gemspec
       Bundle complete! 1 Gemfile dependency, 2 gems now installed.
       Bundled gems are installed into `./.bundle`
       Post-install message from rack:
       Rack's post install message
       # $? => 0
     # ./spec/bundler/friendly_errors_spec.rb:27:in `block (3 levels) in <top (required)>'
     # ./spec/spec_helper.rb:109:in `block (3 levels) in <top (required)>'
     # ./spec/spec_helper.rb:109:in `block (2 levels) in <top (required)>'
     # ./spec/spec_helper.rb:76:in `block (2 levels) in <top (required)>'
     # ./spec/support/rubygems_ext.rb:98:in `load'
     # ./spec/support/rubygems_ext.rb:98:in `gem_load_and_activate'
     # ./spec/support/rubygems_ext.rb:45:in `gem_load'
```

My fix is to make this test independent from the specific rubygems
configuration in the main test process.

1 files changed, 2 insertions, 2 deletions

diff --git a/spec/bundler/friendly_errors_spec.rb b/spec/bundler/friendly_errors_spec.rb
index e9189b0514..82553a3ca7 100644
--- a/spec/bundler/friendly_errors_spec.rb
+++ b/spec/bundler/friendly_errors_spec.rb
@@ -7,13 +7,13 @@ require "cgi"
 RSpec.describe Bundler, "friendly errors" do
   context "with invalid YAML in .gemrc" do
     before do
-      File.open(Gem.configuration.config_file_name, "w") do |f|
+      File.open(home(".gemrc"), "w") do |f|
         f.write "invalid: yaml: hah"
       end
     end
 
     after do
-      FileUtils.rm(Gem.configuration.config_file_name)
+      FileUtils.rm(home(".gemrc"))
     end
 
     it "reports a relevant friendly error message" do