Stop running tests on python 2.7 and 3.6

2.7 stopped working after b69f81d.

3.6 seems to not work: https://github.com/nico/ninjatracing/actions/runs/5720226961/job/15499732849?pr=29

Author: nico

.github/workflows/test.yml

@@ -9,7 +9,7 @@ jobs:
 
     strategy:
       matrix:
-        python-version: [2.7, 3.6, 3.7, 3.8]
+        python-version: [3.7, 3.8]
     steps:
     - uses: actions/checkout@v2
     - name: Set up Python ${{ matrix.python-version }}