Fix set up encryption toast to use "set up" as action

This changes the "set up encryption" toast to use "set up" as the primary action
button, instead of "upgrade". Other toasts that do use text about upgrading will
keep their primary action text of "upgrade" as before.

Fixes https://github.com/vector-im/riot-web/issues/13231

src/components/views/toasts/SetupEncryptionToast.js

@@ -90,6 +90,7 @@ export default class SetupEncryptionToast extends React.PureComponent {
     getSetupCaption() {
         switch (this.props.kind) {
             case 'set_up_encryption':
+                return _t('Set up');
             case 'upgrade_encryption':
             case 'upgrade_ssss':
                 return _t('Upgrade');