Add multicol-2.vim

https://www.w3.org/TR/2024/WD-css-multicol-2-20241219/

after/syntax/css/multicol-2.vim

@@ -0,0 +1 @@
+syn keyword cssPseudoClassId contained column

test/test.css

@@ -720,6 +720,10 @@ mask {
   display: balance-all;
 }
 
+.multicol-2::column {
+	display: auto:
+}
+
 .namespace-3 {
   display: auto;
 }