Fix merged line comments (#13438)

changelog_unreleased/javascript/13438.md

@@ -0,0 +1,16 @@
+#### Fix interleaved comments (#13438 by @thorn0)
+
+<!-- prettier-ignore -->
+```js
+// Input
+function x() {
+} // first
+; // second
+
+// Prettier stable
+function x() {} // first // second
+
+// Prettier main
+function x() {} // first
+// second
+```