RuboCop: Set `EncforcedStyle: use_perl_names` for `Style/SpecialGlobalVars`

What does this MR do and why?

This MR tweaks Style/SpecialGlobalVars's configuration to use EncforcedStyle: use_perl_names. See !83879 (comment 899367028) for the reason.

There's a follow-up RuboCop: Switch to `EncforcedStyle: use_builti... (#358427 - closed) to switch back to EncforcedStyle: use_english_names.

Refs #275984 (comment 893014914)

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