ci: prevent pushing sha images to the registry in docker workflow

[hazre]

Description

Fixes #

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

[github-actions]

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sable: patch
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[github-actions]

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Status	Preview URL	Commit	Alias	Updated (UTC)
✅ Deployment successful!	https://pr-121-sable.raspy-dream-bb1d.workers.dev	eae1955	pr-121	Tue, 10 Mar 2026 04:20:56 GMT