Add mailcap to dependencies

Without `/etc/mime.types` (from mailcap) or alternatively
`/usr/share/mime/globs2` (created by the pacman hook of
shared-mime-info), Caddy will not set a `Content-Type` header for the
files it serves.

See https://wiki.archlinux.org/title/Caddy#Missing_Content-Type

PKGBUILD

@@ -15,6 +15,7 @@ arch=(x86_64)
 license=(Apache-2.0)
 depends=(
   glibc
+  mailcap
 )
 makedepends=(
   git