cgen: fix in map_literal (fix #8868) (#8871)

vlib/builtin/map_test.v

@@ -626,3 +626,9 @@ fn test_map_assign_empty_map_init() {
 	assert a == map[string]int{}
 	assert '$a' == '{}'
 }
+
+fn test_in_map_literal() {
+	assert 1 in map{
+		1: 'one'
+	}
+}

vlib/v/checker/checker.v

@@ -745,11 +745,12 @@ pub fn (mut c Checker) infix_expr(mut infix_expr ast.InfixExpr) table.Type {
 					}
 				}
 				.map {
-					elem_type := right.map_info().key_type
-					c.check_expected(left_type, elem_type) or {
+					map_info := right.map_info()
+					c.check_expected(left_type, map_info.key_type) or {
 						c.error('left operand to `$infix_expr.op` does not match the map key type: $err',
 							left_right_pos)
 					}
+					infix_expr.left_type = map_info.key_type
 				}
 				.string {
 					c.check_expected(left_type, right_type) or {