Fix type infeerence for ICollection

[MartinGC94]

PR Summary

Fixes type inference when accessing indexes of ICollection types like System.Security.AccessControl.AuthorizationRuleCollection for scenarios like (Get-Acl).Access[0].<Tab>
It looks like someone switched two variables around by mistake. I also added a comment to the if statement to explain why it's not doing something the "obvious" way.

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[daxian-dbw]

LGTM

[ghost]

🎉v7.3.0-preview.7 has been released which incorporates this pull request.:tada:

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