default.json: use config:best-practices

```
  'best-practices': {
    configMigration: true,
    description:
      'Preset with best practices from the Renovate maintainers. Recommended for advanced users, who want to follow our best practices.',
    extends: [
      'config:recommended',
      'docker:pinDigests',
      'helpers:pinGitHubActionDigests',
      ':pinDevDependencies',
    ],
  },
...
  recommended: {
    description:
      'Recommended configuration for most users. It does not matter what programming language you use.',
    extends: [
      ':dependencyDashboard',
      ':semanticPrefixFixDepsChoreOthers',
      ':ignoreModulesAndTests',
      'group:monorepos',
      'group:recommended',
      'replacements:all',
      'workarounds:all',
    ],
  },
```

default.json

@@ -1,8 +1,7 @@
 {
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
   "extends": [
-    "config:base",
-    "helpers:pinGitHubActionDigests"
+    "config:best-practices"
   ],
   "packageRules": [
     {