ca55-south is upside down in the test (#1223)

not a big issue since it's only a test, but I can't unsee it

Author: Fil

test/output/contourCa55.svg

@@ -7,7 +7,7 @@ async function plotCa55(mark) {
   return Plot.plot({
     width: 640,
     height: 484,
-    projection: {type: "identity", inset: 3, domain},
+    projection: {type: "reflect-y", inset: 3, domain},
     color: {type: "diverging"},
     marks: [mark(ca55)]
   });