Fix not being able to scale apps within groups

[adersberger]

If you try to scale an app which is grouped together with other apps (and has dependencies to other apps) this won't work (error: "app XY does not exist"). See cloud-native-zwitscher-jee as reproducer. No reproduction steps.

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This issue still violates some of our guidelines:

• Issue title must be in imperative, present tense (e.g. "add", "fix", "change") (?)

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Thank you, everything looks good now!