Add myself to mailmap

Some tool used `Samuel "Sam" Tardieu` as a full name in some of the
commits imported along with clippy.

.mailmap

@@ -494,6 +494,7 @@ Ryan Sullivant <[email protected]>
 Ryan Wiedemann <[email protected]>
 S Pradeep Kumar <[email protected]>
 Sam Radhakrishnan <[email protected]>
+Samuel Tardieu <[email protected]>
 Scott McMurray <[email protected]>
 Scott Olson <[email protected]> Scott Olson <[email protected]>
 Sean Gillespie <[email protected]> swgillespie <[email protected]>