Store ctest output from all ranks in CI as GitLab artifacts

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[msimberg]

cscs-ci run

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cscs-ci run

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cscs-ci run

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cscs-ci run

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cscs-ci run

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This seems to be working nicely. All ranks now have verbose test output, but only rank 0 actually outputs to the terminal. All ranks store the output to a file that's stored as an artifact. For example, https://gitlab.com/cscs-ci/ci-testing/webhook-ci/mirrors/4700071344751697/7514005670787789/-/jobs/8288337613 had test_multiplication_hermitian fail again with a segfault. The main output says srun: error: nid01590: task 2: Exited with exit code 1. If one then goes to the artifacts and looks at the log for rank 2 (ctest.2.txt: https://gitlab.com/cscs-ci/ci-testing/webhook-ci/mirrors/4700071344751697/7514005670787789/-/jobs/8288337613/artifacts/external_file/output/ctest.2.txt) it'll say in the backtrace:
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60: Backtrace:
60: /opt/spack/opt/spack/linux-ubuntu24.04-x86_64/clang-15.0.7/mimalloc-2.1.7-rn6y2rsalkj2ojyubzejabtelannsbga/lib/libmimalloc.so.2(__libc_free+0x10)[0x7ffff69456c0]
60: /DLA-Future-build/lib/libgtest.so.1.13.0(_ZN7testing8UnitTest13PopGTestTraceEv+0xba)[0x7ffff6c67fea]
60: /DLA-Future-build/lib/libgtest.so.1.13.0(_ZN7testing11ScopedTraceD1Ev+0x18)[0x7ffff6c6aef8]
60: /DLA-Future-build/test/unit/multiplication/test_multiplication_hermitian(+0x7162a)[0x5555555c562a]
60: /DLA-Future-build/test/unit/multiplication/test_multiplication_hermitian(+0x7126e)[0x5555555c526e]
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with PopGTestTrace already quite a good hint as to what's going on. Not all failures actually print this, but at least there's higher chance of seeing it now.

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cscs-ci run