patch 8.1.2239: CI fails when running tests without building Vim

Problem:    CI fails when running tests without building Vim.
Solution:   Skip creating doc tags if the execute does not exist.
diff --git a/src/version.c b/src/version.c
index e1d5c64..d0f62e9 100644
--- a/src/version.c
+++ b/src/version.c
@@ -742,6 +742,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2239,
+/**/
     2238,
 /**/
     2237,