patch 8.2.0066: some corners of vim_snprintf() are not tested

Problem:    Some corners of vim_snprintf() are not tested.
Solution:   Add a test in C. (Dominique Pelle, closes #5422)
diff --git a/src/version.c b/src/version.c
index 85fdf1a..b86424f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -743,6 +743,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    66,
+/**/
     65,
 /**/
     64,