Ignore renovate updates for ubuntu and ubuntu-devcontainer

Something like:
```json

{
"packageRules": [
{
"matchManagers": ["dockerfile"],
"matchDatasources": ["docker"],
"matchPackageNames": ["ubuntu", "ubuntu-devcontainer"],
"matchUpdateTypes": ["digest"],
"enabled": false
}
]
}
```

Find the repository's Renovate configuration and review its existing package rules. Add a rule matching Dockerfile-managed Ubuntu and ubuntu-devcontainer digest updates, then verify the configuration parses and those digest updates are disabled without affecting other update types.

Vom Indexierungsmodell aus dem Issue-Text verfasst.