Replace red-herring warning around process aliasing get-process with warning around invalid syntax

[bergmeister]

PR Summary

Fixes #1402 by not warning around process aliasing get-process but rather that there is likely invalid syntax around the proces block since it is technically not possible to execute process as a command.

It would be better to have a rule of it's own for checking the begin/process/end blocks within a scriptblock but issue #1571 tracks this. This PR fixes the red-herring warning, whilst also giving a better warning to the user in the short term.

PR Checklist

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