tests: fix shellcheck warning in test

tests/main/snapctl-is-connected-pid/task.yaml

@@ -54,12 +54,15 @@ execute: |
     expect_status 10 test-snap2.snapctl is-connected --pid 1 foo-slot
 
     if [[ "$(snap debug confinement)" = strict ]]; then
-      svc_label=$(cat "/proc/$svc_pid/attr/current" | sed 's/ (.*)$//')
+      svc_label=$(sed 's/ (.*)$//' < "/proc/$svc_pid/attr/current")
 
       echo "We can detect connected interfaces by AppArmor label too"
       test-snapd2.snapctl is-connected --apparmor-label "$svc_label" foo-slot
       snap connect test-snap1:foo-plug test-snap2:foo-slot
       expect_status 1 test-snap2.snapctl is-connected --apparmor-label "$svc_label" foo-slot
+
+      echo "Non-snap AppArmor labels return a special exit code"
+      expect_status 10 test-snap2.snapctl is-connected --apparmor-label /usr/bin/evince foo-slot
     fi
 
     # The remaining tests rely on classic confinement, so skip Ubuntu Core