Core: Ensure forms in tests have some actual content

Empty forms have no height, so they're considered hidden in jquery-git as of
jquery/jquery@10399dd

Author: scottgonzalez

tests/unit/core/core.html

@@ -42,8 +42,13 @@
 	<area shape="rect" coords="1,1,2,2" href="foo.html" id="areaNoImg" alt="">
 </map>
 
-<form id="formNoTabindex"></form>
-<form id="formTabindex" tabindex="1"></form>
+<form id="formNoTabindex">
+	<input>
+</form>
+
+<form id="formTabindex" tabindex="1">
+	<input>
+</form>
 
 <div>
 	<input id="visibleAncestor-inputTypeNone">