Add easing-2.vim

https://www.w3.org/TR/2024/WD-css-easing-2-20240829/

after/syntax/css/easing-2.vim

@@ -0,0 +1 @@
+syn region cssFunction contained matchgroup=cssFunctionName start="\<linear\s*(" end=")" oneline  contains=cssValueInteger,cssValueNumber,cssValueLength,cssFunctionComma

test/test.css

@@ -336,6 +336,10 @@
 	display: auto;
 }
 
+.easing-2 {
+	display: linear(0, 0.25, 1);
+}
+
 .exclusions-3 {
 	wrap-flow: auto;
 	wrap-through: auto;