Update container to install the cvs dependency

This should allow diff [1] to build.

[1] D5988

Related to T2845

base-buster/Dockerfile

@@ -30,6 +30,7 @@ RUN --mount=type=cache,id=apt-cache,target=/var/cache/apt --mount=type=cache,id=
   arcanist \
   build-essential \
   cassandra \
+  cvs \
   elasticsearch \
   fuse3 \
   git-lfs \

[Phabricator Migration user]

Some references in the commit message have been migrated:

• D5988 is now swh/devel/swh-loader-cvs!69 (closed)