fix syntax (#392)

src/specklepy/objects/geometry/mesh.py

@@ -49,9 +49,8 @@ class Mesh(
 
         if len(self.vertices) % 3 != 0:
             raise ValueError(
-                f"Invalid vertices list: length ({
-                    len(self.vertices)
-                }) must be a multiple of 3"
+                f"Invalid vertices list: length {len(self.vertices)} "
+                f"must be a multiple of 3"
             )
         return len(self.vertices) // 3