Fix crash when expect_corrections runs into an infinite loop

[dvandersluis]

The message for InfiniteCorrectionLoop was changed in #8701, but it now crashes if expect_corrections in a spec causes an infinite loop:

Failure/Error:
  root_cause = offenses_by_iteration[loop_start..-1]
               .map { |x| x.map(&:cop_name).uniq.join(', ') }
               .join(' -> ')

NoMethodError:
  undefined method `map' for nil:NilClass
# ./lib/rubocop/runner.rb:18:in `initialize'
# ./lib/rubocop/rspec/expect_offense.rb:160:in `new'
# ./lib/rubocop/rspec/expect_offense.rb:160:in `block in expect_correction'
# ./lib/rubocop/rspec/expect_offense.rb:150:in `loop'
# ./lib/rubocop/rspec/expect_offense.rb:150:in `expect_correction'

This fixes that crash by capturing the offenses in expect_offenses and passing them into RuboCop::Runner::InfiniteCorrectionLoop.new.

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[bbatsov]

Thanks!