Don't require sidekiq-middleware in fixture file that doesn't use it

What does this MR do?

The ./spec/support/sidekiq_middleware file doesn't seem to be required to run the db/fixtures/development/25_api_personal_access_token.rb fixture. This MR removes it.

Issue: #300613

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Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
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• Tested in all supported browsers
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Security

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