fix: update parameter type annotation for embed_documents method

Author: a-klos

libs/rag-core-api/src/rag_core_api/impl/embeddings/stackit_embedder.py

@@ -46,7 +46,7 @@ def embed_documents(self, texts: list[str]) -> list[list[float]]:
 
         Parameters
         ----------
-        texts : list of str
+        texts : list[str]
             A batch of texts to be embedded.
 
         Returns