reproducibly_build_Tails_ISO_* Jenkins job fails to run diffoscope on non-reproducible builds ⇒ relevant artifacts are not collected

From the log:

[...]
15:56:27 + sudo TMPDIR=/var/lib/jenkins/workspace/reproducibly_build_Tails_ISO_feature-bullseye diffoscope --text /var/lib/jenkins/workspace/reproducibly_build_Tails_ISO_feature-bullseye/build-artifacts/diffoscope.iso.txt --html /var/lib/jenkins/workspace/reproducibly_build_Tails_ISO_feature-bullseye/build-artifacts/diffoscope.iso.html --max-report-size 262144000 --max-diff-block-lines 10000 --max-diff-input-lines 10000000 --profile=- /var/lib/jenkins/workspace/reproducibly_build_Tails_ISO_feature-bullseye/build-artifacts/1/tails-amd64-feature_bullseye@60abfa6399+devel@a8e6d05cf3-20211122T1459Z.iso /var/lib/jenkins/workspace/reproducibly_build_Tails_ISO_feature-bullseye/build-artifacts/2/tails-amd64-feature_bullseye@60abfa6399+devel@a8e6d05cf3-20211130T1533Z.iso
15:56:27 FATAL: command execution failed
15:57:30 java.nio.channels.ClosedChannelException
15:57:30 	at org.jenkinsci.remoting.protocol.NetworkLayer.onRecvClosed(NetworkLayer.java:154)
15:57:30 	at org.jenkinsci.remoting.protocol.impl.NIONetworkLayer.ready(NIONetworkLayer.java:142)
15:57:30 	at org.jenkinsci.remoting.protocol.IOHub$OnReady.run(IOHub.java:792)
15:57:30 	at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:28)
15:57:30 	at jenkins.security.ImpersonatingExecutorService$1.run(ImpersonatingExecutorService.java:68)
15:57:30 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
15:57:30 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
15:57:30 	at java.lang.Thread.run(Thread.java:748)
15:57:30 Caused: java.io.IOException: Backing channel 'JNLP4-connect connection from isobuilder5.iguana/192.168.126.2:35808' is disconnected.
[...]

So diffoscope seems to immediately fail. Too much RAM needed that early?

This issue makes it harder to work on tails#18692 (closed).