testsuite: Add another repeat node test case

testsuite/gsk/compare/repeat-negative-coords.node

@@ -0,0 +1,8 @@
+repeat {
+  bounds: 0 0 20 10;
+
+  child: container {
+    color { color: blue; bounds: 0 5 10 10;}
+    color { color: red;  bounds: 0 10 10 10;}
+  }
+}

testsuite/gsk/meson.build

@@ -60,6 +60,7 @@ compare_render_tests = [
   'repeat',
   'repeat-texture',
   'repeat-no-repeat',
+  'repeat-negative-coords',
 ]
 
 # these are too sensitive to differences in the renderers