patch 8.2.3500: Github CI fails to install clang

Problem:    Github CI fails to install clang.
Solution:   Install llvm-11 explicitly. (Christian Brabandt, closes #8993)
diff --git a/src/version.c b/src/version.c
index 8497e7d..e09abfa 100644
--- a/src/version.c
+++ b/src/version.c
@@ -758,6 +758,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3500,
+/**/
     3499,
 /**/
     3498,