Add spelling correction for leadin.

Author: cfi-gb

codespell_lib/data/dictionary.txt

@@ -35931,6 +35931,7 @@ lcuase->clause
 leaast->least
 leace->leave
 leack->leak
+leadin->leading, lead in,
 leagacy->legacy
 leagal->legal
 leagalise->legalise