Bug 1580908 - Part 11: Fix test_size_of_rule_node. r=emilio

Apparently I made SourcePropertyDeclaration 8 bytes shorter by updating
arrayvec. (see
bluss/arrayvec@b56c3b7
and
bluss/arrayvec@2901223
for details)

Differential Revision: https://phabricator.services.mozilla.com/D45746

--HG--
extra : moz-landing-system : lando

servo/ports/geckolib/tests/size_of.rs

@@ -60,7 +60,7 @@ size_of_test!(test_size_of_rule_node, RuleNode, 80);
 size_of_test!(
     test_size_of_parsed_declaration,
     style::properties::SourcePropertyDeclaration,
-    608
+    600
 );
 
 size_of_test!(test_size_of_computed_image, computed::image::Image, 16);