State mutations must be synchronous. Using a promise.then handler to set the background is a violation of that.
Co-authored-by: kolaente <k@knt.li>
Co-authored-by: Dominik Pschenitschni <mail@celement.de>
Reviewed-on: https://kolaente.dev/vikunja/frontend/pulls/858
Co-authored-by: konrad <k@knt.li>
Co-committed-by: konrad <k@knt.li>