You can configure a system to make use of this repository, thus: 
$ sudo tee /etc/apt/sources.list.d/salsa-rrdtool-team-rrdtool-8567973.sources >/dev/null <<EOF
Types: deb
URIs: https://salsa.debian.org/rrdtool-team/rrdtool/-/jobs/8567973/artifacts/raw/aptly
Suites: unstable
Components: main
Signed-By:
 -----BEGIN PGP PUBLIC KEY BLOCK-----
 .
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 hycxdjA7BhA5nxwZEo7Wf1jVIK1f6FfEhmXkuMdluZcTPTgHm/KUGfghIuWHbM5t
 5DwTKcqUhPGqSAksGDF6TVwB/wM8ZxJNvxQJNBQQgMPXrc0xo637f0aDNjPlmYiP
 TPpAkGY030NvY2c9+Tf6xInyPgkFaTsfvatNK2AiFAh9DIIODklKtNJIMB0b9yPy
 teLuYlDhhe8t1GLIEBr8DYb9K9fz+rqlgTFMReF+j/z0b/I26CqHjT8nempOVkYP
 l/fUv8JiANr6l1RJLuQ7qux6kLjvTZW0MDIxABEBAAG0KlNhbHNhIFBpcGVsaW5l
 IDxzYWxzYS1waXBlbGluZUBkZWJpYW4ub3JnPokBTwQTAQoAORYhBEAqfOqJ4F6f
 IqJkcjo47f0wU+/4BQJpD9EwAxsvBAULCQgHAgYVCgkICwIEFgIDAQIeAQIXgAAK
 CRA6OO39MFPv+IQZB/9QNkN1QEQ7UrSR1YQIlYO8fuTwc43PI71pJPmJhXBBSaMp
 UbVeGkYbB7877eMsyqw45TmhfQWl8KoN9PmKUrX4kLdRwHDHH9s2lw2soK8AARCd
 wjcSMEWNdbX1eX20xLSWGypL8eVIlTo0IJU9PaDRPbOfSujX9gfRNphI2IDrhpTD
 QFOKCEWd6nfLvMuF4eSpPriYYFJLOcyiD0sJD2QHpoOUxdjg9VOWbwaIcVZnGcBj
 YDTwCyD4+ryoslR3X2PX7HoMm58DT4Xt+rwU4+m+W5L7fzo5NYPQMwE3RzLvmFfd
 3FSX+L4/j3DhRhTgqsJlxxQ8WhVtMGN99ktbNnNQ
 =/x8Q
 -----END PGP PUBLIC KEY BLOCK-----
EOF

Alternatively, using the old one-line format, thus: 
$ wget -O - https://salsa.debian.org/rrdtool-team/rrdtool/-/jobs/8567973/artifacts/raw/aptly/public-key.asc | sudo tee /etc/apt/keyrings/salsa-rrdtool-team-rrdtool-8567973.asc >/dev/null
$ sudo tee /etc/apt/sources.list.d/salsa-rrdtool-team-rrdtool-8567973.list >/dev/null <<EOF
deb [signed-by=/etc/apt/keyrings/salsa-rrdtool-team-rrdtool-8567973.asc] https://salsa.debian.org/rrdtool-team/rrdtool/-/jobs/8567973/artifacts/raw/aptly unstable main
# deb-src [signed-by=/etc/apt/keyrings/salsa-rrdtool-team-rrdtool-8567973.asc] https://salsa.debian.org/rrdtool-team/rrdtool/-/jobs/8567973/artifacts/raw/aptly unstable main
EOF

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