Fix env duplication on merged-usr systems #1184

Job	Run time
Tests (macos-14, aarch64-apple-darwin, yes)	12m 58s
Builds (macos-14, aarch64-apple-darwin, yes)	2m 55s
Tests in Containers (ci-jupyter-container, ubuntu-latest, mcr.microsoft.com/devcontainers/univers...	3m 54s
Tests (windows-latest, x86_64-pc-windows-msvc, yes)	7m 48s
Builds (windows-latest, aarch64-pc-windows-msvc)	4m 10s
Builds (macos-latest, x86_64-apple-darwin, yes)	1m 55s
Builds (windows-latest, x86_64-pc-windows-msvc)	4m 47s
Builds (ubuntu-latest, x86_64-unknown-linux-musl, yes)	1m 53s
Env Tests (ci-poetry-global, ubuntu-latest, x86_64-unknown-linux-musl)	2m 37s
Env Tests (ci-poetry-project, windows-latest, x86_64-pc-windows-msvc)	5m 10s
Env Tests (ci-poetry-global, windows-latest, x86_64-pc-windows-msvc)	4m 45s
Tests (ubuntu-latest, x86_64-unknown-linux-musl, yes)	8m 50s
Env Tests (ci-poetry-project, ubuntu-latest, x86_64-unknown-linux-musl)	2m 44s
Env Tests (ci-poetry-custom, windows-latest, x86_64-pc-windows-msvc)	5m 2s
Env Tests (ci-poetry-custom, ubuntu-latest, x86_64-unknown-linux-musl)	2m 41s
Tests in Containers (ci-homebrew-container, ubuntu-latest, homebrew/brew, x86_64-unknown-linux-musl)	3m 42s
Tests (macos-latest, x86_64-apple-darwin, yes)	15m 36s
	1h 31m 27s

Provide feedback