[release-1.10] fix bug preventing AKS autoscaling from being disabled

[k8s-infra-cherrypick-robot]

This is an automated cherry-pick of #3766

/assign mboersma

NONE

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (56ea445) 54.05% compared to head (8d7a26f) 54.05%.
Report is 3 commits behind head on release-1.10.

Additional details and impacted files

@@              Coverage Diff              @@
##           release-1.10    #3771   +/-   ##
=============================================
  Coverage         54.05%   54.05%           
=============================================
  Files               186      186           
  Lines             18833    18833           
=============================================
  Hits              10181    10181           
  Misses             8105     8105           
  Partials            547      547           

Files Changed	Coverage Δ
azure/scope/managedmachinepool.go	42.70% <100.00%> (ø)
azure/services/agentpools/spec.go	57.86% <100.00%> (ø)

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[mboersma]

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 92d4dad75f9b19a8444aaa9715b389e1bfec170b

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mboersma

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