Fix nushell completion when using shell integration

[ruoyouz]

What do you want to change?

Currently completion in nushell does not work for commands wrapped by the shell integration script because they lack the attr complete external flag. See #12008

The fix is very simple, I only need to add @complete external to the two locations in the nu script. I have verified this indeed fixes the issue.

Why do you want to make this change?

The nushell integration breaks completion for commands it redefines, namely ssh and sudo. Considering quite a few commands require elevated privilege, this is less than ideal.

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[jcollie]

!vouch