indexer: Add swh bullseye debian repo for runtime dependency

The fossology license indexer requires the fossology-nomossa package.

As a pre-requisite, it was ported from the buster package:
```
root@pergamon:.../repository# reprepro copy bullseye-swh buster-swh fossology-nomossa
Exporting indices...
root@pergamon:.../repository# reprepro ls fossology-nomossa | grep bull
fossology-nomossa | 3.1-1~bpo10~swh+1 | bullseye-swh | amd64
```

Related to T4540