Fix RuboCop offenses for Style/ClassEqualityComparison

What does this MR do?

In !55110 (merged) we've enabled the 👮 Style/ClassEqualityComparison and postponed the fix because the current auto-correct could potentially produce broken code. See the upstream issue which also links the fix.

However, this MR fixes the remaining offenses manually.

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • [-] I have included a changelog entry.
  • I have not included a changelog entry because it's developer-facing.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content