Tests that the safe-area-(max-)inset-* environment variables can be overridden in OOPIFs.
iframe loaded, overriding insets
Environment:
safe-area-inset-top: 1
safe-area-max-inset-top: 2
safe-area-inset-left: 3
safe-area-max-inset-left: 4
safe-area-inset-bottom: 5
safe-area-max-inset-bottom: 6
safe-area-inset-right: 7
safe-area-max-inset-right: 8