workspace: update to Go 1.21.5

Change-Id: I651588c482518205895cebd5975e52388d66940f
Reviewed-on: https://review.monogon.dev/c/monogon/+/2593
Tested-by: Jenkins CI
Reviewed-by: Tim Windelschmidt <tim@monogon.tech>
diff --git a/WORKSPACE b/WORKSPACE
index 8bc9c00..be413fc 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -84,7 +84,7 @@
 go_rules_dependencies()
 
 go_register_toolchains(
-    go_version = "1.21.4",
+    go_version = "1.21.5",
     nogo = "@dev_source_monogon//build/analysis:nogo",
 )