Fixes for broken CI builds (#3276)

* Install dev requirements when running unit tests

* Disable mysql and postgresql checks for pull requests

* Install required dev packages when running tests on docker build

.github/workflows/docker.yaml

@@ -45,6 +45,7 @@ jobs:
       - name: Run Unit Tests
         run: |
           docker-compose run inventree-dev-server invoke update
+          docker-compose run inventree-dev-server invoke pip3 install -U -r requirements-dev.txt
           docker-compose up -d
           docker-compose run inventree-dev-server invoke wait
           docker-compose run inventree-dev-server invoke test