Multi-platform actions for Python (#583)

.github/workflows/python.yml

@@ -45,10 +45,11 @@ defaults:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
 
     strategy:
       matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
         python-version: [3.6, 3.7, 3.8, 3.9]
 
     steps:
@@ -59,10 +60,12 @@ jobs:
       with:
         python-version: ${{ matrix.python-version }}
 
+    - name: Pre-build dependencies specific to Ubuntu
+      if: runner.os == 'Linux'
+      run: sudo apt install libsndfile1-dev
+
     - name: Pre-build dependencies
-      run: |
-        sudo apt install libsndfile1-dev
-        python -m pip install --upgrade pip
+      run: python -m pip install --upgrade pip
 
     - name: Install dependencies
       run: pip install -r requirements.txt