meta: update mailmap for LakshmiSwethaG

LakshmiSwethaG's name appears twice in AUTHORS. Use .mailmap to map the
various email addresses to a single one.

PR-URL: https://github.com/nodejs/node/pull/40172


Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>