patch 8.2.4137: Vim9: calling import with and without method is inconsistent

Problem:    Vim9: calling import with and without method is inconsistent.
Solution:   Set a flag that a parenthsis follows to compile_load_scriptvar().
            Add some more tests.  Improve error message.
diff --git a/src/version.c b/src/version.c
index b2e7429..67e9ca5 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4137,
+/**/
     4136,
 /**/
     4135,