Create GitHub Actions workflow

.github/workflows/build.yml

@@ -0,0 +1,26 @@
+name: Build
+
+on: [push, pull_request]
+
+jobs:
+  install:
+
+    strategy:
+      matrix:
+        os: [ macos-10.15 ]
+
+    runs-on: ${{ matrix.os }}
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Copy formulae
+      run: cp *.rb $(brew --prefix)/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/
+    - name: Install
+      # We install the IIO Oscilloscope package, which builds the others
+      # through dependency resolution.
+      run: brew install --verbose --build-from-source iio-oscilloscope
+    - name: Test
+      run: |
+        for formula in *.rb; do
+          brew test "${formula%.rb}"
+        done