Incorrect visual order of account settings sections and sub sections

[ChristophWurst]

Steps to reproduce

1. Add an account
2. Open account settings

Expected behavior

Mail server appears bigger than IMAP Settings, because it's a parent > child hierarchy.

Actual behavior

IMAP server appears bigger.
That's because both are h3s but the Mail server section is sized down by NcAppSettingsSection.

Mail app version

v5.x

Nextcloud version

No response

Mailserver or service

No response

Operating system

No response

PHP engine version

None

Nextcloud memory caching

No response

Web server

None

Database

None

Additional info

No response