move to python3.8, as 3.6 reached EOL and GH actions don't support it

Author: filyp

.github/workflows/benchamrk.yml

@@ -16,10 +16,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v3
-    - name: Set up Python 3.6
+    - name: Set up Python 3.8
       uses: actions/setup-python@v4
       with:
-        python-version: '3.6'
+        python-version: '3.8'
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip

.github/workflows/python-app.yml

@@ -18,10 +18,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v3
-    - name: Set up Python 3.6
+    - name: Set up Python 3.8
       uses: actions/setup-python@v4
       with:
-        python-version: '3.6'
+        python-version: '3.8'
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip