Fix build with clang 12 (#4920)

src/ds/files.h

@@ -136,7 +136,10 @@ namespace files
     if (ec)
     {
       throw std::logic_error(fmt::format(
-        "Could not rename file {} to {}: {}", src, dst, ec.message()));
+        "Could not rename file {} to {}: {}",
+        src.string(),
+        dst.string(),
+        ec.message()));
     }
   }
 }