Tune cross-signing toasts when 4S is missing

For the case where cross-signing is trusted on device but secret storage does
not exist, we were showing "verify this device", which is not the best match
from the existing toasts. This tunes the checks to instead show "set up
encryption" which is at least a bit closer.

Part of https://github.com/vector-im/element-web/issues/14970

src/DeviceListener.ts

@@ -220,7 +220,10 @@ export default class DeviceListener {
             await cli.downloadKeys([cli.getUserId()]);
             // cross signing isn't enabled - nag to enable it
             // There are 3 different toasts for:
-            if (cli.getStoredCrossSigningForUser(cli.getUserId())) {
+            if (
+                !cli.getCrossSigningId() &&
+                cli.getStoredCrossSigningForUser(cli.getUserId())
+            ) {
                 // Cross-signing on account but this device doesn't trust the master key (verify this session)
                 showSetupEncryptionToast(SetupKind.VERIFY_THIS_SESSION);
             } else {