reftests: Actually add a text-shadow to the text-shadow reftest

The reftest still passes, since the code still works, but we might as
well test what we claim to test.

testsuite/reftests/Makefile.am

@@ -301,6 +301,7 @@ testdata = \
 	label-sizing.ui \
 	label-small-ellipsized.ref.ui \
 	label-small-ellipsized.ui \
+	label-text-shadow-clipping.css \
 	label-text-shadow-clipping.ref.ui \
 	label-text-shadow-clipping.ui \
 	label-width-chars-dont-shrink.ref.ui \

testsuite/reftests/label-text-shadow-clipping.css

+@import "reset-to-defaults.css";
+
+GtkLabel {
+  font-size: 40px;
+  text-shadow: 20px 20px tomato;
+}