fix python version

.github/workflows/pull_request-test-python.yaml

@@ -12,11 +12,11 @@ jobs:
     strategy:
       matrix:
         python-version:
-        - 2.7
-        - 3.5.7
-        - 3.6.9
-        - 3.7.5
-        - 3.8.0
+        - 2.7.17
+        - 3.5.9
+        - 3.6.10
+        - 3.7.6
+        - 3.8.1
     steps:
     - name: Set up Python
       uses: actions/setup-python@v1