ci: fix renovate config parsing

[phisco]

Description of your changes

Fixes #7174

I have:

• Read and followed Crossplane's contribution process.
• Run ./nix.sh flake check to ensure this PR is ready for review.
• Added or updated unit tests.
• Added or updated e2e tests.
• Linked a PR or a docs tracking issue to document this change.
• Added backport release-x.y labels to auto-backport this PR.
• Followed the API promotion workflow if this PR introduces, removes, or promotes an API.

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[jbw976]

seems reasonable, thanks @phisco! can you also share how you were able to validate this?

[phisco]

Just running the command didn't load all the files for some reason, so I had to pass them all manually, the warnings are fine as they are supposed to be merged:

$ npx --yes --package renovate -- renovate-config-validator --strict .github/renovate-base.json5 .github/renovate-earthly.json5 .github/renovate-nix.json5 .github/renovate.json5

 INFO: Validating .github/renovate-base.json5
 INFO: Validating .github/renovate-earthly.json5
 WARN: Found errors in configuration
       "file": ".github/renovate-earthly.json5",
       "warnings": [
         {
           "topic": "Configuration Error",
           "message": "packageRules[0]: You must configure baseBranches inorder to use them inside matchBaseBranches."
         },
         {
           "topic": "Configuration Error",
           "message": "packageRules[1]: You must configure baseBranches inorder to use them inside matchBaseBranches."
         }
       ]
 INFO: Validating .github/renovate-nix.json5
 WARN: Found errors in configuration
       "file": ".github/renovate-nix.json5",
       "warnings": [
         {
           "topic": "Configuration Error",
           "message": "packageRules[0]: You must configure baseBranches inorder to use them inside matchBaseBranches."
         },
         {
           "topic": "Configuration Error",
           "message": "packageRules[1]: You must configure baseBranches inorder to use them inside matchBaseBranches."
         }
       ]
 INFO: Validating .github/renovate.json5