1.2 — Pass the DB engine into `import_generators` (stop the OEP fallback)

[joda9]

• File: edisgo/run/tasks/flex.py → task_import_generators (~line 277)
• Branch: fix/import-generators-engine

Problem. task_import_generators calls edisgo.import_generators(...)
without engine; EDisGo.import_generators (edisgo.py ~line 1006:
engine = kwargs["engine"] if "engine" in kwargs else egon_engine()) then falls
back to the OEP engine. All sibling tasks already pass engine=ctx.ensure_engine().

@@ def task_import_generators
     edisgo.import_generators(
-        generator_scenario=generator_scenario or ctx.scenario
+        generator_scenario=generator_scenario or ctx.scenario,
+        engine=ctx.ensure_engine(),
     )
     return edisgo

Verify. During import_generators the local-DB engine log line appears (no
"Getting OEP token" / openenergyplatform.org).

Part of #665.