Fix some usages of check_runner_upgrade_status

What does this MR do and why?

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This MR addresses 500 error when fetching runner list in admin pa... (#367829 - closed) which was introduced by Return suggested version along with recommendation (!92126 - merged). It fixes some usages of Gitlab::Ci::RunnerUpgradeCheck#check_runner_upgrade_status which were missed in the original MR.

In that MR, Gitlab::Ci::RunnerUpgradeCheck#check_runner_upgrade_status was changed so that it returns a tuple of { <status>: <version> } instead of simply <status>, but some usages were missed.

I will open a follow-up MR to add more integration tests to make sure something like this doesn't easily happen in the future.

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