fix(config): migrate language objects

[rarkins]

Changes

Context

Closes #23155

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• Code inspection only, or
• Newly added/modified unit tests, or
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• Both unit tests + ran on a real repository

[rarkins]

DEBUG: Config migration necessary (repository=renovate-reproductions/top-level-migrate)
       "oldConfig": {
         "docker": {"pinDigests": true},
         "dotnet": {"packageRules": [{"matchPackageNames": ["foo"], "enabled": false}]}
       },
       "newConfig": {
         "packageRules": [
           {"matchCategories": ["docker"], "pinDigests": true},
           {
             "matchCategories": ["dotnet"],
             "matchPackageNames": ["foo"],
             "enabled": false
           }
         ]
       }

[renovate-release]

🎉 This PR is included in version 36.0.3 🎉

The release is available on:

• GitHub release
• 36.0.3

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