fix: add launcher entrypoint for CNB images on dokku run and cron:run

The scheduler-run script classified CNB-based images as `herokuish` because
`is_image_herokuish_based` returns true for them, which caused the
`docker-args-process-run` trigger for builder-pack to skip injecting
`--entrypoint launcher`. Without that flag the container fell back to the
image entrypoint (`/cnb/process/web`) and dropped the user-supplied
arguments. Mirror the deploy-side detection so CNB images set
`IMAGE_SOURCE_TYPE=pack`, allowing the launcher entrypoint to be added.

tests/apps/python/app-cnb-cron-procfile.json

@@ -0,0 +1,21 @@
+{
+  "cron": [
+    {
+      "command": "task",
+      "schedule": "5 5 5 5 5"
+    }
+  ],
+  "healthchecks": {
+    "web": [
+      {
+        "attempts": 2,
+        "content": "python/http.server",
+        "name": "check-1",
+        "path": "/",
+        "timeout": 5,
+        "type": "startup",
+        "wait": 2
+      }
+    ]
+  }
+}