Missing qoute

Author: sverhoeven

.github/workflows/tests.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: ['ubuntu-latest', 'macos-latest', 'windows-latest]
+        os: ['ubuntu-latest', 'macos-latest', 'windows-latest']
         python-version: ['3.6', '3.7', '3.8', '3.9']
     steps:
     - uses: actions/checkout@v2