Fix env duplication on merged-usr systems #999

Job	Run time
Tests in Containers (ci-jupyter-container, ubuntu-latest, mcr.microsoft.com/devcontainers/univers...	4m 2s
Tests (windows-latest, x86_64-pc-windows-msvc, yes)	10m 35s
Builds (windows-latest, x86_64-pc-windows-msvc)	3m 38s
Tests in Containers (ci-homebrew-container, ubuntu-latest, homebrew/brew, x86_64-unknown-linux-musl)	3m 9s
Env Tests (ci-poetry-global, ubuntu-latest, x86_64-unknown-linux-musl)	2m 26s
Tests (ubuntu-latest, x86_64-unknown-linux-musl, yes)	7m 55s
Builds (windows-latest, aarch64-pc-windows-msvc)	3m 53s
Env Tests (ci-poetry-project, ubuntu-latest, x86_64-unknown-linux-musl)	2m 29s
Tests (macos-latest, x86_64-apple-darwin, yes)	8m 50s
Builds (ubuntu-latest, x86_64-unknown-linux-musl, yes)	1m 52s
Env Tests (ci-poetry-custom, ubuntu-latest, x86_64-unknown-linux-musl)	2m 6s
Builds (macos-latest, x86_64-apple-darwin, yes)	2m 16s
Env Tests (ci-poetry-global, windows-latest, x86_64-pc-windows-msvc)	4m 22s
Tests (macos-14, aarch64-apple-darwin, yes)	8m 24s
Builds (macos-14, aarch64-apple-darwin, yes)	1m 39s
Env Tests (ci-poetry-project, windows-latest, x86_64-pc-windows-msvc)	6m 27s
Env Tests (ci-poetry-custom, windows-latest, x86_64-pc-windows-msvc)	6m 9s
	1h 20m 12s

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