Exclude automatic variable FormatEnumerationLimit from analysis by PSAvoidGlobalVars and PSUseDeclaredVarsMoreThanAssignments

[bergmeister]

PR Summary

Fixes #1756 by adding 1756 to the list of automatic variables that are excluded by PSAvoidGlobalVars and PSUseDeclaredVarsMoreThanAssignments. I don't think this warrants adding a test but I did a quick manual test though that Invoke-ScriptAnalyzer -ScriptDefinition '$FormatEnumerationLimit = 2' and Invoke-ScriptAnalyzer -ScriptDefinition '$global:FormatEnumerationLimit = 2' do not return a warning. Not urgently needed for 1.21.0 so could wait.

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