ci: Fix dependabot config

[mydea]

Apparently, github only validates the dependabot config after merging it 🤦

See https://github.com/getsentry/sentry-javascript/pull/6227/checks?check_run_id=9569642709. Apparently there is no real way to check this beforehand.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.52 KB (+0.08% 🔺)
@sentry/browser - ES5 CDN Bundle (minified)	60.37 KB (+0.07% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.17 KB (+0.1% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	53.72 KB (+0.05% 🔺)
@sentry/browser - Webpack (gzipped + minified)	19.91 KB (+0.07% 🔺)
@sentry/browser - Webpack (minified)	65.18 KB (+0.12% 🔺)
@sentry/react - Webpack (gzipped + minified)	19.94 KB (+0.12% 🔺)
@sentry/nextjs Client - Webpack (gzipped + minified)	45.89 KB (+0.04% 🔺)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	26.33 KB (+0.06% 🔺)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	24.74 KB (+0.07% 🔺)