fix paging if sendmail command writes to file

[Konfekt]

When using Msmtpq instead of Msmtp, this command

https://github.com/marvinthepa/mutt-ical/blob/cba522e6de66d34d4e215fdcd0707e21f7970562/mutt-ical.py#L224

seems to send the mail through a pager (maybe of interest that $LESSOPEN = | lesspipe.sh %s using bat at times) , so that the lines in the mail file in ~/.msmtp.queue are all numbered. With Msmtp this mutt-ical.py (used for answering appointment requests under Mutt) works fine. Since this seems rather odd to me, any explications are welcome.

The sendmail command, either string or function reference, confused the script. In line 222 there was

Incompatible types in assignment (expression has type "str | None", target has type "str | Header")

once commented out, there was no more paging.

The crucial fix seems to be

sendmail = lambda: arg.split()  # If -s is provided, override sendmail with a lambda that returns the command

instead of

sendmail = arg.split()