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 Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME) 2.0.0p1 Checkmk Raw (CRE), Checkmk Enterprise (CEE), Checkmk MSP (CME)

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

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