test(scorecard): preserve CR when retrying on conflict (backport #912)

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Fixes: #841

Description of the change:

• Avoids overwriting the cr variable when calling Update. If this fails due to a conflict, the update will be silently retried, but cr will now be nil.
• Moves the update and retry to a helper function for convenience

Motivation for the change:

• Fixes a sporadic scorecard test failure encountered downstream

How to manually test:

1. make test-scorecard-local SCORECARD_TEST_SELECTION=cryostat-config-change
2. In order to reliably reproduce the update conflict, you can use a patch similar to the one listed here: [Bug] Scorecard test can fail with "failed to get Cryostat CR: resource name may not be empty" #841 (comment)

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This is an automatic backport of pull request #912 done by [Mergify](https://mergify.com).