CI: Simplify workflow

Author: mrkn

.github/workflows/ci.yml

@@ -1,11 +1,18 @@
 name: CI
 
 on:
-- push
+  push:
+    branches:
+    - master
+  pull_request:
+    types:
+    - opened
+    - synchronize
+    - reopened
 
 jobs:
   test:
-    name: Test
+    name: ${{ matrix.os }}/ruby-${{ matrix.ruby }}/python-${{ matrix.python }}-${{ matrix.python_architecture }}
     runs-on: ${{ matrix.os }}
 
     strategy:
@@ -14,12 +21,12 @@ jobs:
         os:
         - ubuntu-18.04
         - macos-latest
-        ruby_version:
-        - 2.7.x
-        - 2.6.x
-        - 2.5.x
-        - 2.4.x
-        python_version:
+        ruby:
+        - 2.7
+        - 2.6
+        - 2.5
+        - 2.4
+        python:
         - 3.8.x
         - 3.7.x
         - 3.6.x
@@ -28,40 +35,30 @@ jobs:
         - x64
 
     steps:
-      - name: Setup Ruby
-        if: matrix.ruby_version != 'master-nightly'
-        uses: actions/setup-ruby@v1
-        with:
-          ruby-version: ${{ matrix.ruby_version }}
+    - uses: actions/checkout@v1
+      with:
+        fetch-depth: 1
+
+    - uses: ruby/setup-ruby@v1
+      if: matrix.ruby_version != 'master-nightly'
+      with:
+        ruby-version: ${{ matrix.ruby }}
 
-      - name: Setup Python
-        uses: actions/setup-python@v1
-        with:
-          python-version: ${{ matrix.python_version }}
-          architecture: ${{ matrix.python_architecture }}
+    - uses: actions/setup-python@v1
+      with:
+        python-version: ${{ matrix.python }}
+        architecture: ${{ matrix.python_architecture }}
 
-      - name: Checkout
-        uses: actions/checkout@v1
-        with:
-          fetch-depth: 1
+    - run: gem install bundler
 
-      - name: Prepare environment
-        run: |
-          gem install bundler
+    - run: pip install --user numpy
 
-      - name: Install requirements
-        run: |
-          pip install --user numpy
-          bundle install
+    - run: bundle install
 
-      - name: Compile pycall.so
-        run: |
-          bundle exec rake compile
+    - run: bundle exec rake compile
 
-      - name: Python investigator
-        run: |
-          python lib/pycall/python/investigator.py
+    - run: python lib/pycall/python/investigator.py
 
-      - name: Test
-        run: |
-          PYTHON=python bundle exec rake
+    - run: bundle exec rake
+      env:
+        PYTHON: python