vertex[patch]: support mistral-small-2503 in model garden (#793)

* add to _MISTRAL_MODELS

* temporarily subset integration tests

* Revert "temporarily subset integration tests"

This reverts commit 1602958.

Author: ccurme

libs/vertexai/langchain_google_vertexai/model_garden_maas/_base.py

@@ -34,6 +34,7 @@
     "mistral-nemo@2407",
     "mistral-large@2407",
     "mistral-large-2411@001",
+    "mistral-small-2503@001",
     "codestral-2501@001",
 ]
 _LLAMA_MODELS: List[str] = [