refactor: update _prepare_texts_to_embed to return a list instead of a dictionary

Author: garybadwal

integrations/google_genai/src/haystack_integrations/components/embedders/google_genai/document_embedder.py

@@ -120,7 +120,7 @@ def from_dict(cls, data: Dict[str, Any]) -> "GoogleGenAIDocumentEmbedder":
         deserialize_secrets_inplace(data["init_parameters"], keys=["api_key"])
         return default_from_dict(cls, data)
 
-    def _prepare_texts_to_embed(self, documents: List[Document]) -> Dict[str, str]:
+    def _prepare_texts_to_embed(self, documents: List[Document]) -> List[str]:
         """
         Prepare the texts to embed by concatenating the Document text with the metadata fields to embed.
         """