Update selectors: credentials dialog, declarative migration assistant

[zbynek]

• Updates selectors to match latest release of credentials dialog (follow-up for Use new dialog design for adding credentials credentials-plugin#500 )
• Updates selector for Declarative Migration Assistant (follow-up for use prism api plugin declarative-pipeline-migration-assistant-plugin#232)

Testing done

Observed that CI passed

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1. Make sure you are opening from a **topic/feature/bugfix branch** (right side) and not your main branch!

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3. Please describe what you did

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