fix(ci): configure Ubuntu box prewarming

- Use the Molecule Ubuntu SSH settings when creating its linked-clone master
- Bound a prewarm SSH failure to ten minutes
- Verify the generated Vagrantfile in the master-preparation fixture

.github/scripts/prepare-vagrant-box-masters.sh

@@ -70,9 +70,19 @@ write_prewarm_vagrantfile() {
     printf '%s\n' "Vagrant.configure('2') do |config|"
     printf '  config.vm.box = "%s"\n' "$box"
     printf '  config.vm.box_version = "%s"\n' "$version"
+    # generic/ubuntu2204 does not accept Vagrant's bundled insecure key.
+    # Match the repository's Molecule connection settings for the short-lived
+    # prewarm clone so Vagrant can record its linked-clone master.
+    if [[ "$box" == 'generic/ubuntu2204' ]]; then
+      printf '%s\n' \
+        '  config.ssh.username = "vagrant"' \
+        '  config.ssh.password = "vagrant"' \
+        '  config.ssh.insert_key = false'
+    fi
     printf '%s\n' \
       '  config.vm.synced_folder ".", "/vagrant", disabled: true' \
       '  config.vm.hostname = "k3s-ansible-box-prewarm"' \
+      '  config.vm.boot_timeout = 600' \
       '  config.vm.provider "virtualbox" do |virtualbox|' \
       '    virtualbox.linked_clone = true' \
       '    virtualbox.memory = 512' \