Werk #12549: Fix parent scan

Component	Setup
Title	Fix parent scan
Date	Mar 15, 2021
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	2.1.0b1 Checkmk Community, Checkmk Pro, Checkmk Ultimate MT 2.0.0p1 Checkmk Community, Checkmk Pro, Checkmk Ultimate MT

The parent scan job always failed with an exception like "TypeError: tuple indices must be integers or slices, not str".

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