fix some CI things

Author: apoelstra

contrib/test.sh

@@ -20,6 +20,7 @@ fi
 if [ "$MSRV" = true ]; then
     cargo update -p url --precise 2.2.2
     cargo update -p form_urlencoded --precise 1.0.1
+    cargo update -p once_cell --precise 1.13.1
 fi
 
 # Format if told to