set python-version to 3.6.15 to satisfy linters

Author: edquist

.github/workflows/python-linters.yml

@@ -22,7 +22,7 @@ jobs:
     - name: Set up Python 3.6
       uses: actions/setup-python@v2
       with:
-        python-version: 3.6
+        python-version: 3.6.15
 
     - uses: actions/cache@v2
       with:
@@ -51,7 +51,7 @@ jobs:
     - name: Set up Python 3.6
       uses: actions/setup-python@v2
       with:
-        python-version: 3.6
+        python-version: 3.6.15
 
     - uses: actions/cache@v2
       with: