[ARM] `az deployment what-if`: Fix an issue where formatting nested array changes throws an exception

[shenglol]

Related command az deployment what-if

Description A customer reported an issue where the what-if command throws an exception when formatting nested array changes. The PR fixes the bug.

Testing Guide az deployment what-if ...

History Notes

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• [x] The PR title and description has followed the guideline in Submitting Pull Requests.

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[yonzhan]

ARM