Fix the soft_fail_count_by_state feature flag

What does this MR do?

IssuableFinder may be used in project or group contexts. While adding a feature flag, I assumed we could use parent to pick either, but it doesn't work.

A feature flag was just added directly above my own, which uses params.group || params.project. I've verified locally (the tests customarily just check blanket en/disablement) that this incantation works as expected.

No need for a changelog, since this is just an inability to selectively turn on a feature flag that isn't documented.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• Documentation (if required)
• Code review guidelines
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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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