You can configure a system to make use of this repository, thus: 
$ sudo tee /etc/apt/sources.list.d/salsa-debian-freeradius-6156294.sources >/dev/null <<EOF
Types: deb
URIs: https://salsa.debian.org/debian/freeradius/-/jobs/6156294/artifacts/raw/aptly
Suites: bullseye
Components: main
Signed-By:
 -----BEGIN PGP PUBLIC KEY BLOCK-----
 .
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 YqoytWf0NEOrMnReSz+YLH06AChvqzoxe3SP3aWz5OWDs4Kj7v4YKbK9nGANrxku
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 4v9ckHO3o4dAZXlJYUyGMij2tX1e9H03TnMq7OEHBa5awJHT4A1DN/xzVG07Zs7T
 SvdgBNHixdGg8tneIog7pn0khwiJkRERFvnBABEBAAG0KlNhbHNhIFBpcGVsaW5l
 IDxzYWxzYS1waXBlbGluZUBkZWJpYW4ub3JnPokBTgQTAQoAOBYhBEic+GWzgKg0
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 CL8t2rbVszE//kYmlJkaLOvvUgRQcphWD4vyi8s2zYh4YP432vXYNp8oEsOhgIS0
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 +y3/U2uzHtNGPyr9OEJG2Kz9nbKNkE4uFei6J3wxBCDvQIPYJu2WxlXZxJV267aY
 MpsDYVuDx6G9DvLncg5VWxkry5TrrNdq5tTI2Ow=
 =esoI
 -----END PGP PUBLIC KEY BLOCK-----
EOF

Alternatively, using the old one-line format, thus: 
$ wget -O - https://salsa.debian.org/debian/freeradius/-/jobs/6156294/artifacts/raw/aptly/public-key.asc | sudo tee /etc/apt/keyrings/salsa-debian-freeradius-6156294.asc >/dev/null
$ sudo tee /etc/apt/sources.list.d/salsa-debian-freeradius-6156294.list >/dev/null <<EOF
deb [signed-by=/etc/apt/keyrings/salsa-debian-freeradius-6156294.asc] https://salsa.debian.org/debian/freeradius/-/jobs/6156294/artifacts/raw/aptly bullseye main
# deb-src [signed-by=/etc/apt/keyrings/salsa-debian-freeradius-6156294.asc] https://salsa.debian.org/debian/freeradius/-/jobs/6156294/artifacts/raw/aptly bullseye main
EOF

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