fix: set python on ci to 3.9

Author: skoob13

.github/workflows/ci.yml

@@ -33,7 +33,7 @@ jobs:
             - name: Check formatting with black
               run: |
                   black --check .
-            
+
             - name: Lint with flake8
               run: |
                   flake8 posthog --ignore E501
@@ -54,7 +54,7 @@ jobs:
             - name: Set up Python 3.8
               uses: actions/setup-python@v2
               with:
-                  python-version: 3.8
+                  python-version: 3.9
 
             - name: Install requirements.txt dependencies with pip
               run: |