Fix add GREENBONE_BOT_TOKEN as a secret when not able to inherit (#151)

This adds GREENBONE_BOT_TOKEN as a workflow secret so that build
pipelines that don't rely on inheritance are able to functions by
providing it manually.

.github/workflows/container-build-push-2nd-gen.yml

@@ -61,6 +61,8 @@ on:
         required: false
       GREENBONE_REGISTRY_TOKEN:
         required: false
+      GREENBONE_BOT_TOKEN:
+        required: false
       GREENBONE_REGISTRY_REPLICATION_USER:
         required: false
       GREENBONE_REGISTRY_REPLICATION_TOKEN: