Silently fail to print the warning in version.download if Ultralytics not installed (#105)

* done

Author: Francesco Saverio Zuppichini

roboflow/core/version.py

@@ -3,6 +3,7 @@
 import sys
 import time
 import zipfile
+from importlib import import_module
 
 import requests
 import wget
@@ -158,10 +159,18 @@ def download(self, model_format=None, location=None, overwrite: bool = True):
         self.__wait_if_generating()
 
         if model_format == "yolov8":
-            # we assume the user will want to use yolov8, for now we only support ultralytics=="8.11.0"
-            print_warn_for_wrong_dependencies_versions(
-                [("ultralytics", "<=", "8.0.20")]
-            )
+            # if ultralytics is installed, we will assume users will want to use yolov8 and we check for the supported version
+            try:
+                import_module("ultralytics")
+                print_warn_for_wrong_dependencies_versions(
+                    [("ultralytics", "<=", "8.0.20")]
+                )
+            except ImportError as e:
+                print(
+                    "[WARNING] we noticed you are downloading a `yolov8` datasets but you don't have `ultralytics` installed. Roboflow `.deploy` supports only models trained with `ultralytics<=8.0.20`, to intall it `pip install ultralytics<=8.0.20`."
+                )
+                # silently fail
+                pass
 
         model_format = self.__get_format_identifier(model_format)