test(molecule): update Vagrant boxes to current releases

- Use published Bento boxes for Ubuntu 26.04, Debian 13, and Rocky Linux 10.1.\n- Pin exact VirtualBox amd64 box versions in CI.\n- Remove the obsolete Ubuntu SSH workaround and update fixtures.

molecule/single_node/molecule.yml

@@ -5,14 +5,9 @@ driver:
   name: vagrant
 platforms:
   - name: control1
-    box: generic/ubuntu2204
+    box: bento/ubuntu-26.04
     memory: 4096
     cpus: 4
-    config_options:
-      # We currently can not use public-key based authentication on Ubuntu 22.04,
-      # see: https://github.com/chef/bento/issues/1405
-      ssh.username: vagrant
-      ssh.password: vagrant
     groups:
       - k3s_cluster
       - master