Fix java_binary load for Bazel 9

Load java_binary from @rules_java instead of relying on the native Bazel
symbol. Bazel 9 removes native Java rules, so java_binary must be loaded
from the external rules_java module.

Change-Id: I4af36ed6233edec2f01818981a80fa577fe65d1a

BUILD

diff --git a/BUILD b/BUILD
index 05555f0..b44326d 100644
--- a/BUILD
+++ b/BUILD
@@ -4,6 +4,7 @@
     "gerrit_plugin_dependency_tests",
     "gerrit_plugin_tests",
 )
+load("@rules_java//java:defs.bzl", "java_binary")
 
 SAML_DEPS = [
     "@saml_plugin_deps//:org_pac4j_pac4j_core",