ci: enable Vagrant-based testing using GitHub Actions

* Semi-automated using https://github.com/myii/ssf-formula/pull/309

.github/workflows/kitchen.vagrant.yml

+# -*- coding: utf-8 -*-
+# vim: ft=yaml
+---
+name: 'Kitchen Vagrant (FreeBSD)'
+'on': ['push', 'pull_request']
+
+env:
+  KITCHEN_LOCAL_YAML: 'kitchen.vagrant.yml'
+
+jobs:
+  test:
+    runs-on: 'macos-10.15'
+    strategy:
+      fail-fast: false
+      matrix:
+        instance:
+          # - default-freebsd-122-latest-py3
+          - freebsd-122-latest-py3
+          # - default-freebsd-114-latest-py3
+          - freebsd-114-latest-py3
+    steps:
+      - name: 'Check out code'
+        uses: 'actions/checkout@v2'
+      - name: 'Set up Bundler cache'
+        uses: 'actions/cache@v1'
+        with:
+          path: 'vendor/bundle'
+          key: "${{ runner.os }}-gems-${{ hashFiles('**/Gemfile.lock') }}"
+          restore-keys: "${{ runner.os }}-gems-"
+      - name: 'Run Bundler'
+        run: |
+          ruby --version
+          bundle config path vendor/bundle
+          bundle install --jobs 4 --retry 3
+      - name: 'Run Test Kitchen'
+        run: 'bundle exec kitchen verify ${{ matrix.instance }}'

Gemfile

 # rubocop:enable Layout/LineLength
 gem 'kitchen-inspec', '>= 2.2.1'
 gem 'kitchen-salt', '>= 0.6.3'
+
+group :vagrant do
+  gem 'kitchen-vagrant'
+end

Gemfile.lock

     kitchen-salt (0.6.3)
       hashie (>= 3.5)
       test-kitchen (>= 1.4)
+    kitchen-vagrant (1.7.0)
+      test-kitchen (>= 1.4, < 3)
     libyajl2 (1.2.0)
     license-acceptance (1.0.19)
       pastel (~> 0.7)
   kitchen-docker!
   kitchen-inspec (>= 2.2.1)
   kitchen-salt (>= 0.6.3)
+  kitchen-vagrant
 
 BUNDLED WITH
    2.1.2

kitchen.vagrant.yml

+# -*- coding: utf-8 -*-
+# vim: ft=yaml
+---
+driver:
+  name: vagrant
+  cache_directory: false
+  customize:
+    usbxhci: 'off'
+  gui: false
+  linked_clone: true
+  ssh:
+    shell: /bin/sh
+
+platforms:
+  - name: freebsd-122-latest-py3
+    driver:
+      box: bento/freebsd-12.2
+  - name: freebsd-114-latest-py3
+    driver:
+      box: bento/freebsd-11.4
+
+provisioner:
+  salt_install: bootstrap