Fix Pietro's entry in the mailmap

Mailmap only allows one remapping per line, so @pietroalbini wasn't
getting grouped correctly. Fix this.

Author: tgross35

Diff for: .mailmap

@@ -474,7 +474,8 @@ Philipp Matthias Schäfer <philipp.matthias.schaefer@posteo.de>
 phosphorus <steepout@qq.com>
 Pierre Krieger <pierre.krieger1708@gmail.com>
 pierwill <pierwill@users.noreply.github.com> <19642016+pierwill@users.noreply.github.com>
-Pietro Albini <pietro@pietroalbini.org> <pietro@pietroalbini.io> <pietro.albini@ferrous-systems.com>
+Pietro Albini <pietro@pietroalbini.org> <pietro@pietroalbini.io>
+Pietro Albini <pietro@pietroalbini.org> <pietro.albini@ferrous-systems.com>
 Pradyumna Rahul <prkinformed@gmail.com>
 Przemysław Wesołek <jest@go.art.pl> Przemek Wesołek <jest@go.art.pl>
 r00ster <r00ster91@protonmail.com>