backup: fix ignoring of harmless borg warnings

backup.py

@@ -377,7 +377,7 @@ def main(argv: list[str]):
             backup.log('E', f"borg exited with signal {-ret}")
         elif ret == 2 or borg_saw_errors:
             backup.log('E', f"borg exited with errors (ret={ret})")
-        elif ret == 1 or borg_saw_warnings:
+        elif ret == 1 and borg_saw_warnings:
             backup.log('W', f"borg exited with warnings (ret={ret})")
         else:
             backup.log('E', f"borg exited with unknown error code {ret}")