Bug 1835066 - Fix a Gecko reftest that isn't valid when nesting is enabled.

See https://github.com/w3c/csswg-drafts/issues/7961#issuecomment-1549874958

In general I agree with Tab that media blocks should parse the same
regardless of whether they are nested.

We should add a test that covers this to WPT, but for now tweak the
local reftest.

MANUAL PUSH: Trivial orange fix CLOSED TREE

layout/reftests/bugs/431948-1.html

@@ -7,16 +7,13 @@ span {
 
 /* A semicolon at the top level of a @media block should not cause the
    whole @media block to be invalidated; in particular, valid rules
-   either before or after it should not be discarded.  (But a rule
-   immediately after the semicolon is consumed by error recovery.)  */
+   either before or after it should not be discarded.  */
 @media screen {
   #a { background-color: green }
   ;
 }
 @media screen {
   #b { background-color: green } 
-  ;
-  #b { background-color: yellow }
   #c { background-color: green }
 }