Fix RuboCop offenses in several ErrorTracking specs

What does this MR do and why?

This MR resolves current and upcoming RuboCop rules in several Category:Error Tracking specs.

Extracted from !85907 (merged).

Please don't squash commits.

Screenshots or screen recordings

n/a

How to set up and validate locally

merge_base=$(git merge-base pl-error-tracking-rubocop-offenses origin/master)
changed=$(git diff --name-only $merge_base | grep -v yml)

$ REVEAL_RUBOCOP_TODO=1 exec rubocop $changed

Inspecting 14 files
.............C

Offenses:

spec/support/shared_contexts/sentry_error_tracking_shared_context.rb:3:22: C: RSpec/ContextWording: Start context description with 'when', 'with', or 'without'.
RSpec.shared_context 'sentry error tracking context' do
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

14 files inspected, 1 offense detected

$ REVEAL_RUBOCOP_TODO=0 bundle exec rubocop $changed
Inspecting 14 files
..............

14 files inspected, no offenses detected

bin/rspec $(tff -f tests.yml $changed)
.........................................................................................

Finished in 18.18 seconds (files took 8.61 seconds to load)
89 examples, 0 failures

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

.rubocop_todo/layout/line_length.yml

@@ -5992,7 +5992,6 @@ Layout/LineLength:
     - 'spec/services/environments/reset_auto_stop_service_spec.rb'
     - 'spec/services/environments/schedule_to_delete_review_apps_service_spec.rb'
     - 'spec/services/environments/stop_service_spec.rb'
-    - 'spec/services/error_tracking/base_service_spec.rb'
     - 'spec/services/events/destroy_service_spec.rb'
     - 'spec/services/feature_flags/create_service_spec.rb'
     - 'spec/services/feature_flags/update_service_spec.rb'