patch 8.1.1951: mouse double click test is a bit flaky

Problem:    Mouse double click test is a bit flaky.
Solution:   Add to list of flaky tests.  Update a couple of comments.
diff --git a/src/version.c b/src/version.c
index 156f075..00e82da 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1951,
+/**/
     1950,
 /**/
     1949,