Fix f-string in add detector endpoint

src/nsls2api/api/v1/beamline_api.py

@@ -112,7 +112,7 @@ async def add_or_delete_detector(
         if new_detector is None:
             raise HTTPException(
                 status_code=409,
-                detail=f"Detector already exists in beamline {name} with either name '{detector.name}' or directory name '[detector.directory_name}'",
+                detail=f"Detector already exists in beamline {name} with either name '{detector.name}' or directory name '{detector.directory_name}'",
             )
 
         changed_detector = new_detector