return this in MailsCollection’s assert methods

[marcuspoehls]

🔗 Linked issue

The same change as in pull request #115.
This time against the 9.x branch.

❓ Type of change

• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This merge request adds a return this to all assertion methods within the MailsCollection class. This mail collection class is returned from the fake mailer. Returning the same instance allows chaining of assertions.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.
• I feel like there’s no documentation needed for this change.

[thetutlage]

Thanks @marcuspoehls 👍🏽