nixosTests.prometheus-exporters.smokeping: fix test after 0.10.0

prometheus-smokeping-prober was updated to 0.10.0 in #396980
which introduced a new label `tos` in its metrics.
add it to the failing tests to make them match
the expected metric (and pass) again

you could argue that the tests are a bit too greedy with the way
they match metrics, but I actually like it that way

(cherry picked from commit 2103ba26886f3e2ac531cdea072d673f3e0ffed3)

nixos/tests/prometheus-exporters.nix

···
         wait_for_open_port(9374)
         wait_until_succeeds(
             "curl -sSf localhost:9374/metrics | grep '{}' | grep -v ' 0$'".format(
-                'smokeping_requests_total{host="127.0.0.1",ip="127.0.0.1",source=""} '
+                'smokeping_requests_total{host="127.0.0.1",ip="127.0.0.1",source="",tos="0"} '
             )
         )
         wait_until_succeeds(
             "curl -sSf localhost:9374/metrics | grep '{}'".format(
-                'smokeping_response_ttl{host="127.0.0.1",ip="127.0.0.1",source=""}'
+                'smokeping_response_ttl{host="127.0.0.1",ip="127.0.0.1",source="",tos="0"}'
             )
         )
       '';