patch 8.2.4069: Vim9: import test fails on MS-Windows

Problem:    Vim9: import test fails on MS-Windows.
Solution:   Ignore case.  Adjust test to avoid name that only differs in case.
diff --git a/src/scriptfile.c b/src/scriptfile.c
index 3508139..56186ff 100644
--- a/src/scriptfile.c
+++ b/src/scriptfile.c
@@ -2156,7 +2156,7 @@
 
     if (p == NULL)
 	return NULL;
-    prefix = vim_strsave(p);
+    prefix = strlow_save(p);
     if (prefix == NULL)
 	return NULL;