fix: AttributeError: module 'frappe' has no attribute 'get_single_value' in older fw versions <16 (backport #1101)

[mergify]

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This is an automatic backport of pull request #1101 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of bc16b92 has failed:

On branch mergify/bp/version-3-hotfix/pr-1101
Your branch is up to date with 'origin/version-3-hotfix'.

You are currently cherry-picking commit bc16b928.
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  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   insights/api/__init__.py

no changes added to commit (use "git add" and/or "git commit -a")

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