Fix to return a boolean value (#4018)

(cherry picked from commit 92cada658a2aaa1e39afed280336644c4c0067ab)

InvenTree/common/models.py

@@ -1372,7 +1372,7 @@ class InvenTreeSetting(BaseInvenTreeSetting):
         'PLUGIN_ON_STARTUP': {
             'name': _('Check plugins on startup'),
             'description': _('Check that all plugins are installed on startup - enable in container environments'),
-            'default': os.getenv('INVENTREE_DOCKER', False),
+            'default': str(os.getenv('INVENTREE_DOCKER', False)).lower() in ['1', 'true'],
             'validator': bool,
             'requires_restart': True,
         },