Unset no-rubygems option for rspec-rails sub-job

Rails do use Gem in rails/railties/lib/rails/ruby_version_check.rb

    if Gem::Version.new(RUBY_VERSION) < Gem::Version.new("2.5.0")

and obviously since RubyGems are loaded by default by recent rubies, it
doesn't care to explicitly require it. That results in:

    /home/runner/work/rspec-expectations/rspec-rails/bin/rspec

    An error occurred while loading spec_helper.
    Failure/Error: require 'rails/all'

    NameError:
      uninitialized constant Gem
    # /home/runner/work/rspec-expectations/bundle/ruby/2.5.0/gems/railties-6.0.3.4/lib/rails/ruby_version_check.rb:3:in `<top (required)>'
    # /home/runner/work/rspec-expectations/bundle/ruby/2.5.0/gems/railties-6.0.3.4/lib/rails.rb:3:in `require'

Author: pirj

ci/script/functions.sh

@@ -187,6 +187,6 @@ function run_all_spec_suites {
   fold "rspec-mocks specs" run_spec_suite_for "rspec-mocks"
   fold "rspec-support specs" run_spec_suite_for "rspec-support"
   if rspec_rails_compatible; then
-    fold "rspec-rails specs" run_spec_suite_for "rspec-rails"
+    fold "rspec-rails specs" (unset RUBYOPT && run_spec_suite_for "rspec-rails")
   fi
 }