integration: cover exit nodes via autogroup:internet ACL (#3212)

TestEnablingExitRoutes runs without an ACL, so tailcfg.FilterAllowAll
hides any policy-path regression. Add a sibling that applies the literal
#3212 policy via hsic.WithACLPolicy after registration and approval,
then asserts each peer carries 0.0.0.0/0 + ::/0 in AllowedIPs and
ExitNodeOption is true — the daemon-derived bool that drives
`tailscale exit-node list`.

Updates #3212

.github/workflows/test-integration.yaml

@@ -239,6 +239,7 @@ jobs:
           - TestHASubnetRouterFailover
           - TestSubnetRouteACL
           - TestEnablingExitRoutes
+          - TestExitRoutesWithAutogroupInternetACL
           - TestSubnetRouterMultiNetwork
           - TestSubnetRouterMultiNetworkExitNode
           - TestAutoApproveMultiNetwork/authkey-tag.*