treewide: update to go 1.21.4

Change-Id: I4f4cdaf696a13dd967834ec5ea690aa266e3aea8
Reviewed-on: https://review.monogon.dev/c/monogon/+/2310
Tested-by: Jenkins CI
Reviewed-by: Leopold Schabel <leo@monogon.tech>
diff --git a/WORKSPACE b/WORKSPACE
index f5560cc..c10f39a 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -84,7 +84,7 @@
 go_rules_dependencies()
 
 go_register_toolchains(
-    go_version = "1.21.0",
+    go_version = "1.21.4",
     nogo = "@dev_source_monogon//build/analysis:nogo",
 )