Bug 1950076 [wpt PR 50903] - Update wpt metadata, a=testonly

wpt-pr: 50903
wpt-type: metadata

UltraBlame original commit: 555984c1024602882e82d8dee6ac8c8e93381338

Author: marco-c

testing/web-platform/meta/css/css-mixins/at-function-parsing.html.ini

@@ -977,3 +977,29 @@ valid
 expected
 :
 FAIL
+[
+function
+-
+-
+foo
+(
+-
+-
+x
+:
+1px
+-
+-
+y
+-
+-
+z
+:
+2px
+)
+is
+valid
+]
+expected
+:
+FAIL