Fix Qt-RangeLoopDetach Axivion warnings in qplacemanagerengineosm.cpp

- use std::as_const() where possible, and introduce an intermediate
  local const variable where it is not.

Axivion-Id: qt_Add-ons_qtlocation_dev_linux:SV267
Axivion-Id: qt_Add-ons_qtlocation_dev_linux:SV268
Axivion-Id: qt_Add-ons_qtlocation_dev_linux:SV269
Axivion-Id: qt_Add-ons_qtlocation_dev_linux:SV270
Task-number: QTBUG-144760
Pick-to: 6.12 6.11 6.8
Change-Id: I9f9172adbc237c0b7a2207f87d97dfbf1484ab90
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>