Extend connectivity check (#308)

Spotted in this gitlab.inria.fr job today:
https://gitlab.inria.fr/math-comp/math-comp/-/jobs/4607507

Author: Zimmi48

src/actions.ml

@@ -512,6 +512,7 @@ let trace_action ~repo_full_name trace =
        || test "HTTP request sent, awaiting response... 50[0-9]"
        || test "The requested URL returned error: 502"
        || test "received unexpected HTTP status: 50[0-9]"
+       || test "unexpected status from GET request to.*: 50[0-9]"
        (*|| test "[Tt]he remote end hung up unexpectedly"*)
        (* Can happen with (actual) issues with overlays. *)
        || test "error: unable to download 'https://cache.nixos.org/"