patch 8.2.4121: Visual test fails on MS-Windows

Problem:    Visual test fails on MS-Windows.
Solution:   Set 'isprint' so that the character used is not printable.
diff --git a/src/version.c b/src/version.c
index 6fda77e..bc75522 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4121,
+/**/
     4120,
 /**/
     4119,