Remove the last occurence of `get_upstream` in the test #4224

Job	Run time
checks / check-style	1m 40s
checks / other-checks	40s
devcontainer / build (amd64, 12.2, conda)	12m 7s
devcontainer / build (amd64, 12.2, pip)	11m 26s
wheel-build-pylibraft	0s
conda-cpp-build	0s
wheel-tests-pylibraft	0s
conda-cpp-tests	0s
conda-cpp-checks	0s
conda-python-build	0s
wheel-build-raft-dask	0s
docs-build	0s
conda-python-tests	0s
wheel-tests-raft-dask	0s
pr-builder	0s
	25m 53s

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