broker: add stopped-preserving upgrade without actor execution

cli/tests/actors/toolbox/src/main.rs

@@ -38,6 +38,10 @@ fn main() {
         panic!("version 2 crashes on startup");
     }
 
+    if actor == "stopped-upgrade" {
+        std::fs::write("/data/main-version", &version).unwrap();
+    }
+
     let mut open = HashMap::<String, std::fs::File>::new();
     // Files that this actor serves at /actor/<id>/fs/ (path -> text).
     let mut served = std::collections::BTreeMap::<String, String>::new();