patch 9.1.0578: no tests for :Tohtml

Problem:  no tests for :Tohtml
Solution: Add two basic tests (Yinzuo Jiang)

closes: #15240

Signed-off-by: Yinzuo Jiang <jiangyinzuo@foxmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index a1b87b3..c87d378 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    578,
+/**/
     577,
 /**/
     576,