[fbsync] Fix missing f-string prefix in error message (#6684)

Summary: Co-authored-by: Nicolas Hug <[email protected]>

Reviewed By: datumbox

Differential Revision: D40138730

fbshipit-source-id: 09187f46ea50364f9374eee0f4e58ae7bb5bf146

Author: NicolasHug

torchvision/models/detection/roi_heads.py

@@ -746,7 +746,7 @@ def forward(
                 if not t["boxes"].dtype in floating_point_types:
                     raise TypeError(f"target boxes must of float type, instead got {t['boxes'].dtype}")
                 if not t["labels"].dtype == torch.int64:
-                    raise TypeError("target labels must of int64 type, instead got {t['labels'].dtype}")
+                    raise TypeError(f"target labels must of int64 type, instead got {t['labels'].dtype}")
                 if self.has_keypoint():
                     if not t["keypoints"].dtype == torch.float32:
                         raise TypeError(f"target keypoints must of float type, instead got {t['keypoints'].dtype}")