[Rails5] Fix optimistic lock value

What does this MR do?

Updates the monkey-patch to make it work in Rails 5.

Fixes the error:

Failures:

  1) IssueSerializer non-sidebar issue serialization matches issue json schema
     Failure/Error: JSON::Validator.validate!(SchemaPath.expand(schema, dir), data, options)

     JSON::Schema::ValidationError:
       The property '#/lock_version' of type integer did not match one or more of the following types: string, null
     # ./spec/support/api/schema_matcher.rb:23:in `block (2 levels) in <top (required)>'
     # ./spec/serializers/issue_serializer_spec.rb:16:in `block (3 levels) in <top (required)>'

Finished in 9 minutes 4 seconds (files took 17.56 seconds to load)
1572 examples, 1 failure, 1 pending

Are there points in the code the reviewer needs to double check?

Do we really want to use NULL instead of 0?

Why was this MR needed?

Migration to Rails 5.0.

Screenshots (if relevant)

No.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #47961 (closed)