cubicweb #12418708 should not return 'cubicweb' [validation pending]

but either an empty string (in which case the cubicweb.mail.format_mail() handles these empty string correctly) or the config value for EMAIL.sender-name, since it seems to be only there to be make InternalManager usable for notification stuff (according to the comment in the code).

This prevent from EMAIL.sender-name to be used as From: in notificatio emails (like in forgotpwd)

done in3.20.15
load left0.000
closed by#f24e83a82a4f [server] make return an empty string (closes #12418708)
patch[server] make return an empty string (closes #12418708) [applied]