You can configure a system to make use of this repository, thus: 
$ sudo tee /etc/apt/sources.list.d/salsa-freexian-team-debusine-7040777.sources >/dev/null <<EOF
Types: deb
URIs: https://salsa.debian.org/freexian-team/debusine/-/jobs/7040777/artifacts/raw/aptly
Suites: bookworm
Components: main
Signed-By:
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EOF

Alternatively, using the old one-line format, thus: 
$ wget -O - https://salsa.debian.org/freexian-team/debusine/-/jobs/7040777/artifacts/raw/aptly/public-key.asc | sudo tee /etc/apt/keyrings/salsa-freexian-team-debusine-7040777.asc >/dev/null
$ sudo tee /etc/apt/sources.list.d/salsa-freexian-team-debusine-7040777.list >/dev/null <<EOF
deb [signed-by=/etc/apt/keyrings/salsa-freexian-team-debusine-7040777.asc] https://salsa.debian.org/freexian-team/debusine/-/jobs/7040777/artifacts/raw/aptly bookworm main
# deb-src [signed-by=/etc/apt/keyrings/salsa-freexian-team-debusine-7040777.asc] https://salsa.debian.org/freexian-team/debusine/-/jobs/7040777/artifacts/raw/aptly bookworm main
EOF

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