Fix typo in FuncAppKeysHelper.cs

[myatt83]

Fix typo in comment: environment variable

Issue describing the changes in this PR

N/A

Pull request checklist

• [X ] My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• [X ] My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• [X ] My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• I have added all required tests (Unit tests, E2E tests)

[liliankasem]

/azp run

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