Try to make CI run for pull requests too

.github/workflows/ci.yml

@@ -1,41 +1,40 @@
 name: CI
 
-on: push
+on: [push, pull_request]
 
 jobs:
-
   build:
     name: Build
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@master
-    - name: Fetch dependencies
-      run: cargo fetch
-    - name: Build in release mode
-      run: cargo build --release --frozen
-  
+      - uses: actions/checkout@master
+      - name: Fetch dependencies
+        run: cargo fetch
+      - name: Build in release mode
+        run: cargo build --release --frozen
+
   test:
     name: Test
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@master
-    - name: Add Ruby for a test that requires it
-      uses: actions/setup-ruby@master
-      with:
-        version: 2.6.x
-    - name: Fetch dependencies
-      run: cargo fetch
-    - name: Build in test mode
-      run: cargo build --tests --frozen
-    - name: Make mask available globally for certain test suites that depend on it
-      run: cp ./target/debug/mask /usr/share/rust/.cargo/bin
-    - name: Run tests
-      run: cargo test --frozen
-  
+      - uses: actions/checkout@master
+      - name: Add Ruby for a test that requires it
+        uses: actions/setup-ruby@master
+        with:
+          version: 2.6.x
+      - name: Fetch dependencies
+        run: cargo fetch
+      - name: Build in test mode
+        run: cargo build --tests --frozen
+      - name: Make mask available globally for certain test suites that depend on it
+        run: cp ./target/debug/mask /usr/share/rust/.cargo/bin
+      - name: Run tests
+        run: cargo test --frozen
+
   format:
     name: Format
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@master
-    - name: Verify formatting is correct
-      run: cargo fmt --all -- --check
+      - uses: actions/checkout@master
+      - name: Verify formatting is correct
+        run: cargo fmt --all -- --check