Change download.apache.org to https://dlcdn.apache.org

That should unstuck the current failing build [1].

[1] https://jenkins.softwareheritage.org/job/jenkins-tools/job/swh-jenkins-dockerfiles/1136/console

Related to T4615

base-buster/Dockerfile

@@ -25,7 +25,7 @@ RUN --mount=type=cache,id=apt-cache,target=/var/cache/apt --mount=type=cache,id=
   echo deb [signed-by=/usr/share/keyrings/elasticsearch-archive-keyring.gpg] https://artifacts.elastic.co/packages/7.x/apt stable main > /etc/apt/sources.list.d/elastic-7.x.list && \
   curl -fsSL https://artifacts.elastic.co/GPG-KEY-elasticsearch | gpg --dearmor > /usr/share/keyrings/elasticsearch-archive-keyring.gpg && \
   echo deb [signed-by=/usr/share/keyrings/cassandra.gpg] https://www.apache.org/dist/cassandra/debian 40x main > /etc/apt/sources.list.d/cassandra.list && \
-  curl -fsSL https://downloads.apache.org/cassandra/KEYS | gpg --dearmor > /usr/share/keyrings/cassandra.gpg && \
+  curl -fsSL https://dlcdn.apache.org/cassandra/KEYS | gpg --dearmor > /usr/share/keyrings/cassandra.gpg && \
   apt-get update && \
   apt-get upgrade -y && \
   apt-get install -y \