Fix `is_writeable()` for 3 OS support (#4743)

* Fix `is_writeable()` for 3 OS support

* Update general.py

utils/general.py

 
 def user_config_dir(dir='Ultralytics'):
     # Return path of user configuration directory (make if necessary)
-    system = platform.system()
-    cfg = {'Windows': 'AppData/Roaming', 'Linux': '.config', 'Darwin': 'Library/Application Support'}
-    path = Path.home() / cfg.get(system, '') / dir
-    if system == 'Linux' and not is_writeable(path):  # GCP functions and AWS lambda solution, only /tmp is writeable
-        path = Path('/tmp') / dir
-    if not path.is_dir():
-        path.mkdir()  # make dir if required
+    cfg = {'Windows': 'AppData/Roaming', 'Linux': '.config', 'Darwin': 'Library/Application Support'}  # 3 config dirs
+    path = Path.home() / cfg.get(platform.system(), '')  # OS-specific config dir
+    path = (path if is_writeable(path) else Path('/tmp')) / dir  # GCP and AWS lambda fix, only /tmp is writeable
+    path.mkdir(exist_ok=True)  # make if required
     return path
 
 
-def is_writeable(path):
-    # Return True if path has write permissions (Warning: known issue on Windows)
-    return os.access(path, os.R_OK)
+def is_writeable(dir):
+    # Return True if directory has write permissions
+    # return os.access(path, os.R_OK)  # known issue on Windows
+    file = Path(dir) / 'tmp.txt'
+    try:
+        with open(file, 'w'):
+            pass
+        file.unlink()  # remove file
+        return True
+    except IOError:
+        return False
 
 
 def is_docker():