Add regression test to ensure that even if JS is enabled but not working, a theme will still get applied

Author: GuillaumeGomez

tests/rustdoc-gui/javascript-disabled.goml

@@ -9,3 +9,12 @@ assert-css: (".sub", {"display": "none"})
 // Even though JS is disabled, we should still have themes applied. Links are never black-colored
 // if styles are applied so we check that they are not.
 assert-css-false: ("a.src", {"color": "#000"})
+
+javascript: true
+fail-on-request-error: false
+block-network-request: "*.js"
+reload:
+
+// JS is enabled but wasn't loaded, we should still have the light theme applied. Links are never
+// black-colored if styles are applied so we check that they are not.
+assert-css-false: ("a.src", {"color": "#000"})