mail/fetchmail: update to 6.6.1

Translation updates by:

• sr: Мирослав Николић [Miroslav Nikolić, Serbian]
• es: Cristian Othón Martínez Vera [Spanish]

PR: 290987
Approved by: Corey Halpin (maintainer)

(reinstated from commit 685e0668a312ae1fbc44aa1635b182c0659718c6,
which got reverted due to missing approval)

(cherry picked from commit 91c9cd805a3cab4b5ac5203cb43f3f6daf1fae52)