Fix pages migration deadlock

What does this MR do?

Fixes #300123 (closed)

Fix is taken from https://guides.rubyonrails.org/threading_and_code_execution.html#permit-concurrent-loads

I can't claim that I understand the underlying behavior, but the deadlock we're catching here looks exactly as described. And in other places where we use Rails.application.executor.wrap, we also use ActiveSupport::Dependencies.interlock.permit_concurrent_loads.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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