Resolve "Improve slow tests in ./spec/features/ide/user_sees_editor_info_spec.rb"

• Step 1 - Handle entry not found in changeFileContent action
• Step 2 - Disallow fs in integration specs
• Step 3 - Resolve "Improve slow tests in ./spec/features/ide/user_sees_editor_info_spec.rb"

What does this MR do?

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• [ ] Changelog entry Not needed since there's no user facing change.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

References

• Related to #282436 (closed)
• Relates to #284930 (closed)