Fix printing of SCSS selector() function (#12213)

changelog_unreleased/scss/12213.md

@@ -0,0 +1,16 @@
+#### Fixes printing parameters of a mixin named `selector()` (#12213 by @duailibe)
+
+<!-- prettier-ignore -->
+```css
+/* Input */
+@mixin selector($param: 'value') {
+}
+
+/* Prettier stable */
+@mixin selector($param: 'value) {
+}
+
+/* Prettier main */
+@mixin selector($param: 'value') {
+}
+```