patch 8.2.0568: the man filetype plugin overwrites the unnamed register

Problem:    The man filetype plugin overwrites the unnamed register.
Solution:   Use the black hole register. (Jason Franklin)
diff --git a/src/version.c b/src/version.c
index d4250e5..5659e92 100644
--- a/src/version.c
+++ b/src/version.c
@@ -739,6 +739,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    568,
+/**/
     567,
 /**/
     566,