ci: pin Node 24 compatible actions

[realies]

Summary

• update GitHub Actions dependencies to Node 24 compatible releases
• pin actions to exact release tags instead of moving major tags
• add Dependabot weekly updates for GitHub Actions

Validation

• YAML parse for workflow and Dependabot config
• bash -n over workflow run scripts
• git diff --check

Note: repository allow_auto_merge is currently false, so Dependabot PR auto-merge still needs repo/ruleset configuration outside dependabot.yml.

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In @.github/workflows/nextcloud-docker.yml:
- Line 125: The actions/checkout reference is pinned to a SHA that maps to tag
v6 (actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10) instead of the
specific v6.0.3 tag; update the uses line
(actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10) to the correct
human-readable pin by replacing the SHA with the explicit tag
actions/checkout@v6.0.3 (or, alternatively, replace it with the exact commit SHA
that GitHub associates with v6.0.3 if you prefer SHA pinning) so the workflow
accurately reflects v6.0.3 and its Node 24 compatibility.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 8bbf651 and 34d9cd9.

📒 Files selected for processing (2)

• .github/dependabot.yml
• .github/workflows/nextcloud-docker.yml