Fix URL for apt.p.o archives.
A new archive repo was created in March of 2020:
@@ -73,7 +73,7 @@ process-max=1
<section id="old-package">
<title>Where can I find packages for older versions of <backrest/>?</title>
- <p>The <link url="https://apt.postgresql.org">apt.postgresql.org</link> repository maintains an <link url="https://atalia.postgresql.org/morgue/p/pgbackrest">archive of older versions</link>. Debian also maintains <link url="https://snapshot.debian.org/binary/pgbackrest/">snapshots</link> of all test builds.</p>
+ <p>The <link url="https://apt.postgresql.org">apt.postgresql.org</link> repository maintains an <link url="https://apt-archive.postgresql.org">archive of older versions</link>. Debian also maintains <link url="https://snapshot.debian.org/binary/pgbackrest/">snapshots</link> of all test builds.</p>
</section>
<section id="backup-standby">
