Bump events-broker version to 3.5.0-alpha-202107290338

Events-broker version 3.5.0-alpha-202107290338 does not support
deserialisation of EventMessages.

Bug: Issue 14823
Change-Id: I38ccae2c246a2b1405ad9d8ad83412a90ce38878

external_plugin_deps.bzl

diff --git a/external_plugin_deps.bzl b/external_plugin_deps.bzl
index 388a15e..50d693f 100644
--- a/external_plugin_deps.bzl
+++ b/external_plugin_deps.bzl
@@ -109,8 +109,8 @@
 
     maven_jar(
         name = "events-broker",
-        artifact = "com.gerritforge:events-broker:3.4.0.4",
-        sha1 = "8d361d863382290e33828116e65698190118d0f1",
+        artifact = "com.gerritforge:events-broker:3.5.0-alpha-202107290338",
+        sha1 = "243ecb0e13c6532a9e3e7ab03d7318cbf350ec77",
     )
 
     maven_jar(