make man-db dependency optional for aur package

[FWDekker]

the aur package currently depends on man-db, but this is not strictly necessary. instead, this dependency should be removed. this requires that the tests support not having man installed. probably an if clause around the part testing man, which checks if a certain environment variable is set, say, MOMMY_TEST_MAN?

[FWDekker]

actually i just realised i can add man-db to the checkdepends and to the optdepends, and then tests will continue to work. any proper aur helper will remove the checkdepends afterwards, so it won't pollute the system, and tests that the installation is correct if the user ever decides to install man-db later on!

[FWDekker]

fixed in the aur repo as described in the comment above