Avoid misdetecting global Linux Python as virtualenv #998

Job	Run time
Tests in Containers (ci-jupyter-container, ubuntu-latest, mcr.microsoft.com/devcontainers/univers...	4m 9s
Builds (windows-latest, x86_64-pc-windows-msvc)	3m 42s
Builds (windows-latest, aarch64-pc-windows-msvc)	3m 33s
Tests in Containers (ci-homebrew-container, ubuntu-latest, homebrew/brew, x86_64-unknown-linux-musl)	3m 12s
Builds (ubuntu-latest, x86_64-unknown-linux-musl, yes)	1m 54s
Builds (macos-latest, x86_64-apple-darwin, yes)	1m 37s
Env Tests (ci-poetry-global, ubuntu-latest, x86_64-unknown-linux-musl)	2m 25s
Builds (macos-14, aarch64-apple-darwin, yes)	1m 41s
Env Tests (ci-poetry-project, ubuntu-latest, x86_64-unknown-linux-musl)	2m 22s
Env Tests (ci-poetry-custom, ubuntu-latest, x86_64-unknown-linux-musl)	2m 24s
Tests (windows-latest, x86_64-pc-windows-msvc, yes)	8m 56s
Env Tests (ci-poetry-global, windows-latest, x86_64-pc-windows-msvc)	4m 25s
Tests (ubuntu-latest, x86_64-unknown-linux-musl, yes)	7m 59s
Tests (macos-latest, x86_64-apple-darwin, yes)	9m 50s
Env Tests (ci-poetry-project, windows-latest, x86_64-pc-windows-msvc)	4m 18s
Tests (macos-14, aarch64-apple-darwin, yes)	9m 17s
Env Tests (ci-poetry-custom, windows-latest, x86_64-pc-windows-msvc)	4m 27s
	1h 16m 11s

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