Ensure that network_mode and networks are not present at the same time

See
https://docs.docker.com/reference/compose-file/services/#network_mode

Signed-off-by: Povilas Kanapickas <povilas@radix.lt>

newsfragments/network_mode_networks.bugfix

@@ -0,0 +1,2 @@
+Improved error detection by rejecting service definitions that contain both "network_mode" and
+"networks" keys, which is not allowed.

podman_compose.py

@@ -880,6 +880,12 @@ async def assert_cnt_nets(compose, cnt):
 def get_net_args_from_network_mode(compose, cnt):
     net_args = []
     net = cnt.get("network_mode")
+    service_name = cnt["service_name"]
+
+    if "networks" in cnt:
+        raise ValueError(
+            f"networks and network_mode must not be present in the same service [{service_name}]"
+        )
 
     is_bridge = False
     if net == "none":

tests/unit/test_get_net_args.py

@@ -59,6 +59,15 @@ class TestGetNetArgs(unittest.TestCase):
         args = get_net_args(compose, container)
         self.assertListEqual(expected_args, args)
 
+    def test_network_mode_and_networks_unsupported(self):
+        compose = get_networked_compose()
+        container = get_minimal_container()
+        container["networks"] = {"net0": {}}
+        container["network_mode"] = "none"
+
+        with self.assertRaises(ValueError):
+            get_net_args(compose, container)
+
     def test_alias(self):
         compose = get_networked_compose()
         container = get_minimal_container()