Harden Panama doctor probes

tests/quickshell/fixtures/doctor/bin/pgrep

@@ -5,6 +5,7 @@ set -euo pipefail
 name="${!#}"
 case ",${PANAMA_DOCTOR_FIXTURE_PROCESSES:-}," in
     *",$name:duplicate,"*) printf '4101\n4102\n' ;;
+    *",$name:malformed,"*) printf 'not-a-pid\n' ;;
     *",$name:missing,"*) exit 1 ;;
     *) printf '4101\n' ;;
 esac