checker: fix dumping match expr (#15869)

vlib/v/checker/checker.v

@@ -2179,6 +2179,7 @@ pub fn (mut c Checker) expr(node_ ast.Expr) ast.Type {
 			return c.concat_expr(mut node)
 		}
 		ast.DumpExpr {
+			c.expected_type = ast.string_type
 			node.expr_type = c.expr(node.expr)
 			c.check_expr_opt_call(node.expr, node.expr_type)
 			etidx := node.expr_type.idx()

vlib/v/tests/inout/dump_match_expr.out

@@ -0,0 +1 @@
+[vlib/v/tests/inout/dump_match_expr.vv:3] ast.MatchExpr: 1

vlib/v/tests/inout/dump_match_expr.vv

@@ -0,0 +1,8 @@
+fn main() {
+	i := 1
+	dump(match i {
+		0 { '0' }
+		1 { '1' }
+		else { '2' }
+	})
+}