fix: typo in exception message for ImproperlyConfiguredException (litestar-org#3885)

Author: Zimzozaur

litestar/di.py

@@ -54,7 +54,7 @@ def __init__(
             sync_to_thread: Run sync code in an async thread. Defaults to False.
         """
         if not callable(dependency):
-            raise ImproperlyConfiguredException("Provider dependency must a callable value")
+            raise ImproperlyConfiguredException("Provider dependency must be a callable value")
 
         is_class_dependency = isclass(dependency)
         self.has_sync_generator_dependency = isgeneratorfunction(