Fix #118906: conflict with alt hotkey in Vert and Edge Slide operators

This 'alt' hotkey is captured in the modal map
`TFM_MODAL_PASSTHROUGH_NAVIGATE` in order to appear in the header.
But this modal map is not necessary.

source/blender/editors/transform/transform.cc

@@ -712,6 +712,13 @@ static bool transform_modal_item_poll(const wmOperator *op, int value)
       break;
     }
     case TFM_MODAL_PASSTHROUGH_NAVIGATE:
+      if (ELEM(t->mode, TFM_EDGE_SLIDE, TFM_VERT_SLIDE)) {
+        /* Returning `false` will not prevent the navigation from working, it will just not display
+         * the shortcut in the header.
+         * Return `false` here to prevent this modal item from affecting the state with
+         * #T_ALT_TRANSFORM used by the Edge and Vert Slide operators. */
+        return false;
+      }
       return t->vod != nullptr;
   }
   return true;