Exposed in the dracut testsuite while adding tests for sysexts:
```
[ 2.972948] localhost (sd-merge)[510]: Validation of dm-verity signature failed via the kernel, trying userspace validation instead: Required key not available
[ 2.972993] localhost (sd-merge)[510]: Skipping file '/etc/verity.d/dracut.pem', suffix is not '.crt'.
[ 2.973045] localhost (sd-merge)[510]: No userspace dm-verity certificates found.
```