Fix a test for bin/bundle update --bundler to pass on ruby/ruby.

[junaruga]

This change to relax the test is to pass make test-bundler on ruby/ruby,
where the system_bundler_version (= Bundler::VERSION) is not the latest version on the RubyGems.
See https://bugs.ruby-lang.org/issues/18643.

What was the end-user or developer problem that led to this PR?

The test can fail in make test-bundler (make test-bundler BUNDLER_SPECS="commands/binstubs_spec.rb") in ruby/ruby, where the Bundler::VERSION is not the latest version in RubyGems.

What is your fix for the problem, implemented in this PR?

I relaxed the matching criteria not depending on the version number.

I tried to use a regular expression seeing the RSpec include method document,
https://relishapp.com/rspec/rspec-expectations/v/3-10/docs/built-in-matchers/include-matcher

expect(out).to include %r(Using bundler \w+\n)

However I see there is a syntax error no implicit conversion of Regexp into String. So, I am just using a string matching.

Make sure the following tasks are checked

• Describe the problem / feature
• Write tests for features and bug fixes
• Write code to solve the problem
• Make sure you follow the current code style and write meaningful commit messages without tags

[junaruga]

Rebased with the implementation to compare the Bundler version. The bin/rubocop on Ruby 3.1.1 shows an issue maybe coming from rubocop itself. Hope the rubocop test passes on CI.

$ ruby -v
ruby 3.1.1p18 (2022-02-18 revision 53f5fc4236) [x86_64-linux]

$ bin/rubocop spec/commands/binstubs_spec.rb
Inspecting 1 file
An error occurred while Layout/BlockAlignment cop was inspecting /home/jaruga/var/git/rubygems/bundler/spec/commands/binstubs_spec.rb:3:0.
To see the complete backtrace run rubocop -d.
.

1 file inspected, no offenses detected

1 error occurred:
An error occurred while Layout/BlockAlignment cop was inspecting /home/jaruga/var/git/rubygems/bundler/spec/commands/binstubs_spec.rb:3:0.
Errors are usually caused by RuboCop bugs.
Please, report your problems to RuboCop's issue tracker.
https://github.com/rubocop-hq/rubocop/issues

Mention the following information in the issue report:
0.80.1 (using Parser 3.1.0.0, running on ruby 3.1.1 x86_64-linux)