Update Python version in CI workflow from 3.6 to 3.8

Author: karlnyr

.github/workflows/run_tests.yml

@@ -15,10 +15,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
-    - name: Set up Python 3.6
+    - name: Set up Python 3.8
       uses: actions/setup-python@v3
       with:
-        python-version: '3.6.15'
+        python-version: '3.8.15'
     - name: Create conda/mamba environment using micromamba
       uses: mamba-org/setup-micromamba@v1
       with: