gci: Re-enable DEVELOPER=0 builds

.ci/test.py

@@ -116,7 +116,6 @@ def run_one(p: Plugin) -> bool:
                 pytest_path,
                 p.path,
                 '-vvv',
-                '-n 5',
                 '--timeout=300',
                 '--junitxml=report-{}.xml'.format(p.name),
                 '--reruns=2',

.github/workflows/main.yml

@@ -18,7 +18,7 @@ jobs:
       fail-fast: false
       matrix:
         python-version: [3.6, 3.7, 3.8]
-        developer: [1]
+        developer: [0,1]
 
     steps:
     - uses: actions/checkout@v2