patch 8.2.3859: Vim9: some code lines not tested

Problem:    Vim9: some code lines not tested.
Solution:   Add a few specific tests.
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 2b27f51..4bce997 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -8333,7 +8333,6 @@
 		lhs_type = parse_type(&p, cctx->ctx_type_list, TRUE);
 	    }
 
-	    // Script var is not supported.
 	    if (get_var_dest(name, &dest, CMD_for, &opt_flags,
 					      &vimvaridx, &type, cctx) == FAIL)
 		goto failed;
@@ -8351,6 +8350,13 @@
 	    }
 	    else
 	    {
+		// Script var is not supported.
+		if (STRNCMP(name, "s:", 2) == 0)
+		{
+		    emsg(_(e_cannot_use_script_variable_in_for_loop));
+		    goto failed;
+		}
+
 		if (!valid_varname(arg, (int)varlen, FALSE))
 		    goto failed;
 		if (lookup_local(arg, varlen, NULL, cctx) == OK)
@@ -8359,12 +8365,6 @@
 		    goto failed;
 		}
 
-		if (STRNCMP(name, "s:", 2) == 0)
-		{
-		    semsg(_(e_cannot_declare_script_variable_in_function), name);
-		    goto failed;
-		}
-
 		// Reserve a variable to store "var".
 		where.wt_index = var_list ? idx + 1 : 0;
 		where.wt_variable = TRUE;