bump vagrant to bullseye (#8)

I tested upgrading from buster to bullseye on vagrant, privatebin works fine.

Co-authored-by: meaz <meaz@disroot.org>
Reviewed-on: #8
Reviewed-by: muppeth <muppeth@no-reply@disroot.org>

Vagrantfile

@@ -8,7 +8,7 @@
 Vagrant.configure("2") do |config|
   #config.ssh.insert_key = false
   config.vm.define "privatebin" do |privatebin|
-    privatebin.vm.box = "generic/debian10"
+    privatebin.vm.box = "generic/debian11"
     privatebin.vm.provider :libvirt do |libvirt|
       libvirt.memory = 256
     end