chore: add min version of Google Auth to include fix

Context: googleapis/python-genai@930c7ca. The GenAI SDK relies on Google Auth for the fix, and adding this as a direct dependency in ADK will decouple the release of ADK and GenAI SDK.

Co-authored-by: Liang Wu <wuliang@google.com>
PiperOrigin-RevId: 852990837

Author: wuliang229

pyproject.toml

@@ -32,6 +32,7 @@ dependencies = [
   "click>=8.1.8, <9.0.0",                                    # For CLI tools
   "fastapi>=0.115.0, <0.124.0",                              # FastAPI framework
   "google-api-python-client>=2.157.0, <3.0.0",               # Google API client discovery
+  "google-auth>=2.47.0",                                     # Google Auth library
   "google-cloud-aiplatform[agent_engines]>=1.132.0, <2.0.0", # For VertexAI integrations, e.g. example store.
   "google-cloud-bigquery-storage>=2.0.0",
   "google-cloud-bigquery>=2.2.0",