Fix version

Vagrantfile

@@ -7,7 +7,7 @@ Vagrant.configure("2") do |config|
   # However, it does not build: https://github.com/precice/vm/issues/83
   # config.vm.box = "generic/ubuntu2004"
   config.vm.box = "bento/ubuntu-20.04"
-  config.vm.box_version = "v202309.09.0"
+  config.vm.box_version = "202309.09.0"
 
   # We don't want the box to automatically update every time it starts.
   # We can instead handle updates internally, without destroying the machine.