patch 8.1.0592: the libvterm tests are not run as part of Vim tests

Problem:    The libvterm tests are not run as part of Vim tests.
Solution:   Add testing libvterm.
diff --git a/src/version.c b/src/version.c
index aafd4cb..4e79d28 100644
--- a/src/version.c
+++ b/src/version.c
@@ -800,6 +800,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    592,
+/**/
     591,
 /**/
     590,