Fix room list scrolling in Safari
Fix room list scrolling in Safari

This sets `flex-basis` properly in Safari so the room list is scrollable.

Fixes https://github.com/vector-im/element-web/issues/14877

matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk