Allow registration to submit for non-fatal errors
Allow registration to submit for non-fatal errors

This allows you to proceed with registration even if the IS is down, for
example.

Fixes https://github.com/vector-im/riot-web/issues/10018

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