Cleanup: Mark overriden virtual call as such

Fixes the `-Winconsistent-missing-override` warning.

In theory the `virtual` is redundant in such case, but this is how
it is done in may other areas of USD code.

Pull Request #104977

source/blender/io/usd/intern/usd_reader_shape.h

@@ -53,7 +53,8 @@ class USDShapeReader : public USDGeomReader {
                   const char ** /*err_str*/) override;
   bool is_time_varying();
 
-  virtual bool topology_changed(const Mesh * /*existing_mesh*/, double /*motionSampleTime*/)
+  virtual bool topology_changed(const Mesh * /*existing_mesh*/,
+                                double /*motionSampleTime*/) override
   {
     return false;
   };