head.hackage: ghc-debugger's test:system-test hangs on test-downstream job

The failure affects both x86-64 and arm64.

Example 1:

https://gitlab.haskell.org/ghc/head.hackage/-/jobs/1769505

Full list:

https://gitlab.haskell.org/ghc/head.hackage/-/jobs?statuses=RUNNING

(and many more)

Since a test timeout is treated as a spurious failure, these get restarted. I think there's around 10 restarts, which results in pipelines taking 80 hours to fail entirely. The result is that many head.hackage pipelines are still running.

https://gitlab.haskell.org/ghc/head.hackage/-/pipelines?page=1&scope=all&status=running

Luckily, the test is merely zombied and doesn't take any system resources. Therefore I'll keep them running for now, so people can investigate. Example process tree:

 489457 ?        S      0:00          \_ bash /nix/store/36qkrsgvqb0scf7hcdr45vz37nbi904x-run-ci
 489516 ?        Sl     0:00              \_ /nix/store/jx4pn482brdqi9fp41m6faawwcibq354-head-hackage-ci-0.1.0.0/bin/head-hackage-ci test-patches --extra-cabal-fragment=/builds/ghc/head.hackage/ci/run/deps.cabal.project --patches=../../patches --with-compiler=/builds/ghc/head.hackage/ghc/bin/ghc --extra-cabal-fragment=/builds/ghc/head.hackage/ci/config.cabal.project --expect-broken=charsetdetect --expect-broken=packman --extra-package=lens==5.2.2 --extra-package=optics==0.4.2.1 --extra-package=aeson==2.2.0.0 --extra-package=criterion==1.6.2.0 --extra-package=scotty==0.12.1 --extra-package=generic-lens==2.2.2.0 --extra-package=microstache==1.0.2.3 --extra-package=singletons-base==3.1.1 --extra-package=servant==0.20 --extra-package=hgmp==0.1.2.1 --extra-package=Agda==2.6.3 --extra-package=mmark==0.0.7.6 --extra-package=doctest==0.22.0 --extra-package=tasty==1.4.3 --extra-package=pandoc==3.1.5 --extra-package=servant-conduit==0.16 --extra-package=servant-machines==0.16 --extra-package=linear-generics==0.2.2 --extra-package=futhark==0.25.2 --extra-package=generic-random==1.5.0.1 --extra-package=lame==0.2.1 --extra-package=inspection-testing==0.5.0.2 --extra-package=ghcide==2.0.0.1 --extra-package=vector-space==0.16 --build-tool-package=alex --build-tool-package=happy --build-tool-package=c2hs --only=tasty --test-package=system-test=/builds/ghc/head.hackage/ci/../tests/ghc-debug/test/ --test-package=ghc-tests=/builds/ghc/head.hackage/ci/../tests/ghc-tests --test-package=all=/builds/ghc/head.hackage/ci/../tests/text --test-package=bytestring-tests=/builds/ghc/head.hackage/ci/../tests/bytestring --test-package=all=/builds/ghc/head.hackage/ci/../tests/containers/containers-tests --cabal-option=-j5 --ghc-option=-dlint
 548483 ?        Sl     0:00                  \_ /nix/store/gwlb8xmagw5a8wam56ja1l0xjpzd139a-cabal-install-3.10.1.0/bin/cabal new-test system-test --enable-tests -j5 -w /builds/ghc/head.hackage/ghc/bin/ghc
 548511 ?        Sl     0:00                      \_ /nix/store/gwlb8xmagw5a8wam56ja1l0xjpzd139a-cabal-install-3.10.1.0/bin/.cabal-wrapped act-as-setup --build-type=Simple -- test --verbose=1 --builddir=/builds/ghc/head.hackage/ci/run/test-system-test/dist-newstyle/build/aarch64-linux/ghc-9.9.20240202/ghc-debugger-0.5.0.0/t/system-test --log=$pkgid-$test-suite.log --machine-log=$pkgid.log --show-details=failures system-test
 548522 ?        Sl     0:00                          \_ /builds/ghc/head.hackage/ci/run/test-system-test/dist-newstyle/build/aarch64-linux/ghc-9.9.20240202/ghc-debugger-0.5.0.0/t/system-test/build/system-test/system-test
 548717 ?        Z      0:00                              \_ [clock] <defunct>