GitHub Actions: Detect operating system with runner.os

Author: cclauss

.github/workflows/tests.yml

@@ -128,7 +128,7 @@ jobs:
           npm install
           pip install pytest
       - name: Set Windows Env
-        if: startsWith(matrix.os, 'windows')
+        if: runner.os == 'Windows'
         run: |
           echo 'GYP_MSVS_VERSION=2015' >> $Env:GITHUB_ENV
           echo 'GYP_MSVS_OVERRIDE_PATH=C:\\Dummy' >> $Env:GITHUB_ENV