postcss-sign-functions: improve abs support (#1514)

Author: romainmenke

packages/css-calc/test/additional/index.mjs

@@ -1,3 +1,4 @@
 import './mod-rem-infinity.mjs';
 import './random.mjs';
+import './sign-abs-equivalent.mjs';
 import './tan-asymptotes.mjs';