Uses postgres on github actions CI

Use a variable set by github to define whether we should use the CI's
postgres as the test database

.github/workflows/build.yml

@@ -38,8 +38,6 @@ jobs:
         run: npm install jasmine-core@2.3.4 karma@1.5 karma-coverage@1.1.1 karma-jasmine@0.3.8 karma-firefox-launcher@2.1.0 karma-coveralls@1.1.2
       - name: Install opal
         run: pip install -e .
-        env:
-          OPAL_TEST_USE_POSTGRES: 1
       - name: Install dependencies
         run: pip install -r test-requirements.txt
       - run: gem install coveralls-lcov

runtests.py

@@ -113,7 +113,7 @@
     }
 )
 
-if os.environ.get('USE_POSTGRES'):
+if os.environ.get('GITHUB_WORKFLOW'):
     test_settings_config["DATABASES"] = {
         'default': {
             'ENGINE': 'django.db.backends.postgresql_psycopg2',