Preserve trailing commas in single-item SCSS lists (#19928)

Co-authored-by: fisker Cheung <lionkay@gmail.com>

changelog_unreleased/scss/19928.md

@@ -0,0 +1,13 @@
+#### Preserve trailing commas in single-item lists (#19928 by @kovsu)
+
+<!-- prettier-ignore -->
+```scss
+// Input
+$list: ("a",);
+
+// Prettier stable
+$list: ("a");
+
+// Prettier main
+$list: ("a",);
+```