chore: use engineering@posthog.com in package metadata

[marandaneto]

💡 Motivation and Context

Composer metadata still uses hey@posthog.com as the package author contact. This updates the published package metadata to use the shared engineering@posthog.com address instead.

💚 How did you test it?

• Verified composer.json now uses engineering@posthog.com
• Confirmed there are no other non-engineering@posthog.com @posthog.com addresses in package metadata files in this repo

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Added the release label to the PR
• Added exactly one version bump label: bump-patch, bump-minor, or bump-major