Fix handling of spaces after for as

crates/compiler/test_syntax/tests/snapshots/pass/pattern_as.expr.result-ast

@@ -7,11 +7,8 @@ When(
             patterns: [
                 @14-20 SpaceBefore(
                     As(
-                        @14-15 SpaceAfter(
-                            Underscore(
-                                "",
-                            ),
-                            [],
+                        @14-15 Underscore(
+                            "",
                         ),
                         PatternAs {
                             spaces_before: [],

crates/compiler/test_syntax/tests/test_fmt.rs

@@ -6113,6 +6113,31 @@ mod test_fmt {
         );
     }
 
+    #[test]
+    fn issue_6215() {
+        expr_formats_to(
+            indoc!(
+                r"
+                when list is
+                    [first as last]
+                    | [first, last]   ->
+                        first
+                    _->Not
+                "
+            ),
+            indoc!(
+                r"
+                when list is
+                    [first as last]
+                    | [first, last] ->
+                        first
+                
+                    _ -> Not
+                "
+            ),
+        );
+    }
+
     // this is a parse error atm
     //    #[test]
     //    fn multiline_apply() {