Fix env duplication on merged-usr systems #1185

Job	Run time
Tests (macos-14, aarch64-apple-darwin, yes)	9m 23s
Builds (windows-latest, aarch64-pc-windows-msvc)	8m 52s
Builds (macos-14, aarch64-apple-darwin, yes)	2m 30s
Tests (ubuntu-latest, x86_64-unknown-linux-musl, yes)	8m 3s
Tests in Containers (ci-jupyter-container, ubuntu-latest, mcr.microsoft.com/devcontainers/univers...	4m 22s
Builds (ubuntu-latest, x86_64-unknown-linux-musl, yes)	2m 18s
Builds (windows-latest, x86_64-pc-windows-msvc)	4m 9s
Tests in Containers (ci-homebrew-container, ubuntu-latest, homebrew/brew, x86_64-unknown-linux-musl)	3m 25s
Tests (macos-latest, x86_64-apple-darwin, yes)	16m 16s
Env Tests (ci-poetry-custom, windows-latest, x86_64-pc-windows-msvc)	5m 2s
Tests (windows-latest, x86_64-pc-windows-msvc, yes)	9m 31s
Env Tests (ci-poetry-custom, ubuntu-latest, x86_64-unknown-linux-musl)	2m 54s
Env Tests (ci-poetry-global, ubuntu-latest, x86_64-unknown-linux-musl)	2m 26s
Env Tests (ci-poetry-project, ubuntu-latest, x86_64-unknown-linux-musl)	2m 49s
Env Tests (ci-poetry-project, windows-latest, x86_64-pc-windows-msvc)	4m 47s
Env Tests (ci-poetry-global, windows-latest, x86_64-pc-windows-msvc)	4m 56s
Builds (macos-latest, x86_64-apple-darwin, yes)	2m 54s
	1h 34m 37s

Provide feedback