patch 8.1.2051: double-click test is a bit flaky

Problem:    Double-click test is a bit flaky.
Solution:   Correct entry in list of flaky tests.
diff --git a/src/version.c b/src/version.c
index a2c5ddd..af656f2 100644
--- a/src/version.c
+++ b/src/version.c
@@ -758,6 +758,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2051,
+/**/
     2050,
 /**/
     2049,