Update test.yml (#689)

* Update test.yml

Fixes failing python 3.6 tests

* Update test.yml

.github/workflows/test.yml

@@ -5,7 +5,7 @@ on: [push, pull_request]
 jobs:
   build:
     name: build (Python ${{ matrix.python-version }}, Django ${{ matrix.django-version }})
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
       matrix:
@@ -37,6 +37,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         python -m pip install --upgrade tox tox-gh-actions
+        python -m pip install setuptools-scm==6.4.2
 
     - name: Tox tests
       run: |