fix(manager/quadlet): enable digest replacement metadata

[AysajanE]

Changes

Enable Quadlet Docker image replacement metadata for tag-and-digest updates and add a focused regression test.

Context

• This closes an existing Issue, Closes: fix(manager/quadlet): pass specifyReplaceString to getDep so docker:pinDigests can pin/update digests #44500
• This doesn't close an Issue, but I accept the risk that this PR may be closed if maintainers disagree with its opening or implementation

AI assistance disclosure

Did you use AI tools to create any part of this pull request?

• No — I did not use AI for this contribution.
• Yes — minimal assistance (e.g., IDE autocomplete, small code completions, grammar fixes).
• Yes — substantive assistance (AI-generated non-trivial portions of code, tests, or documentation).
• Yes — other (please describe):

Codex (OpenAI) was used to generate the code and focused regression test under human review.

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or

• Newly added/modified unit tests, or

• No unit tests, but ran on a real repository, or

• Both unit tests + ran on a real repository

• node_modules/.bin/vitest lib/modules/manager/quadlet/digest-replacement.spec.ts — passed in a network-isolated container.

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AI assistance was used; I reviewed and own this change.

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