fix python versions on actions

Author: magmax

.github/workflows/python-test.yml

@@ -15,7 +15,14 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [2.7, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9]
+        python-version:
+        - "2.7.18"
+        - "3.4.10"
+        - "3.5.10"
+        - "3.6.13"
+        - "3.7.10"
+        - "3.8.8"
+        - "3.9.2"
 
     steps:
     - uses: actions/checkout@v2