Listing which e.g. `debian/*` tag is contained in a `apertis/*` branch
is rather pointless and is a significant waste of resources.

Limit the reported tags to the one with a matching prefix, so only
`debian/*` tags are listed on `debian/*` branches and only `apertis/*`
tags are listed on `apertis/*` branches.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>