Used the version of Ubuntu that still have Python 3.6

Author: D4Vinci

.github/workflows/tests.yml

@@ -7,30 +7,37 @@ concurrency:
 
 jobs:
   tests:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
       matrix:
         include:
         - python-version: "3.6.15"
+          os: ubuntu-20.04
           env:
             TOXENV: py36
         - python-version: "3.7"
+          os: ubuntu-latest
           env:
             TOXENV: py
         - python-version: "3.8"
+          os: ubuntu-latest
           env:
             TOXENV: py
         - python-version: "3.9"
+          os: ubuntu-latest
           env:
             TOXENV: py
         - python-version: "3.10"
+          os: ubuntu-latest
           env:
             TOXENV: py
         - python-version: "3.11"
+          os: ubuntu-latest
           env:
             TOXENV: py
         - python-version: "3.12"
+          os: ubuntu-latest
           env:
             TOXENV: py