fix httpx backend test warning by updating to httpx2

Author: vagkaratzas

backend/pyproject.toml

@@ -13,12 +13,12 @@ dependencies = [
 
 [dependency-groups]
 dev = [
-    "httpx>=0.27.0",
     "pytest>=8.3.0",
     "pytest-asyncio>=0.24.0",
     "mypy>=1.11.0",
     "ruff>=0.6.0",
     "pandas-stubs>=3.0.3.260530",
+    "httpx2>=2.5.0",
 ]
 
 [tool.ruff]