fix ensure namespace is initialized for yielding vars

Author: d-biehl

robotcode/language_server/robotframework/diagnostics/namespace.py

@@ -594,6 +594,8 @@ async def yield_variables(
     ) -> AsyncGenerator[Tuple[VariableMatcher, VariableDefinition], None]:
         from robot.parsing.model.blocks import Keyword, TestCase
 
+        await self.ensure_initialized()
+
         yielded: Dict[VariableMatcher, VariableDefinition] = {}
 
         async for var in async_chain(