Update python-package.yml

Author: samuelduchesne

.github/workflows/python-package.yml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       matrix:
         python-version: [ 3.8 ]
-        os: [ ubuntu-latest ]  # later, add macos-latest, windows-latest
+        os: [ ubuntu-latest, macos-latest, windows-latest ]  # later, add macos-latest, windows-latest
         energyplus-version: [ 9.2.0 ]  # later, add 9.4.0
         include:
           - runs-on: ubuntu-latest