Refactor GitHub Actions workflows

Author: taketo1113

.github/workflows/main.yml renamed to .github/workflows/test.yml

@@ -1,10 +1,8 @@
-name: Ruby
+name: CI
 
 on:
   push:
-    branches:
-      - master
-
+    branches: [ master ]
   pull_request:
 
 jobs:
@@ -25,11 +23,12 @@ jobs:
       RACK_VERSION: ${{ matrix.rack_version }}
 
     steps:
-    - uses: actions/checkout@v4
-    - name: Set up Ruby
-      uses: ruby/setup-ruby@v1
-      with:
-        ruby-version: ${{ matrix.ruby }}
-        bundler-cache: true
-    - name: Run the default task
-      run: bundle exec rake
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby }}
+          bundler-cache: true
+      - name: Run tests
+        run: bundle exec rake