Set up Drone CI, remove Actions configs

.drone.yml

@@ -0,0 +1,16 @@
+kind: pipeline
+name: default
+
+steps:
+- name: specs
+  image: ruby
+  environment:
+    REDIS_HOST: redis
+  commands:
+  - cp config.yml.erb.example config.yml.erb
+  - bundle install --jobs=3 --retry=3
+  - bundle exec rake test
+
+services:
+  - name: redis
+    image: redis

.github/workflows/ruby.yml

@@ -1,33 +0,0 @@
-name: Tests
-
-on:
-  push:
-    branches: [ master ]
-  pull_request:
-    branches: [ master ]
-
-permissions:
-  contents: read
-
-jobs:
-  test:
-    runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        ruby-version: ['2.7', '3.0', '3.1']
-        redis-version: [6, 7]
-    steps:
-    - uses: actions/checkout@v3
-    - name: Set up Ruby
-      uses: ruby/setup-ruby@v1
-      with:
-        ruby-version: ${{ matrix.ruby-version }}
-        bundler-cache: true # runs 'bundle install' and caches installed gems automatically
-    - name: Start Redis
-      uses: supercharge/redis-github-action@1.4.0
-      with:
-        redis-version: ${{ matrix.redis-version }}
-    - name: Configure
-      run: cp config.yml.erb.example config.yml.erb
-    - name: Run tests
-      run: bundle exec rake test