actions: drop unsupported py37 runner

Author: tsani

.github/workflows/tests.yml

@@ -15,7 +15,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: [3.7, 3.8, 3.9, "3.10", "3.11", "pypy-3.7"]
+        python-version: ["3.8", "3.9", "3.10", "3.11", "pypy-3.7"]
 
     env:
       PYTHON: ${{ matrix.python-version }}