[4.0] [a11y] Admin Login Page

[brianteeman]

The a11y team has asked that the login page has a main landmark region

Testing

There should be no visible difference

[zwiastunsw]

I have tested this item ✅ successfully on 7df511d

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[wojsmol]

I have tested this item ✅ successfully on 7df511d

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[Quy]

RTC

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[laoneo]

Thanks

[brianteeman]

Thanks