Allow system interpreters set by `VIRTUAL_ENV` to be used without opt-in #7454

Job	Run time
cargo clippy \| ubuntu	50s
cargo fmt	18s
cargo clippy \| windows	57s
cargo shear	27s
cargo test \| ubuntu	4m 3s
cargo test \| windows	5m 25s
cargo test \| macos	3m 55s
Determine changes	4s
build binary \| linux	1m 11s
build binary \| macos aarch64	1m 25s
build binary \| macos x86_64	1m 30s
build binary \| windows	1m 49s
check windows trampoline	2m 22s
benchmarks	4m 56s
check cache \| ubuntu	54s
integration test \| github actions	7s
integration test \| conda on ubuntu	27s
ecosystem test \| prefecthq/prefect	30s
ecosystem test \| pallets/flask	16s
check system \| python on debian	41s
check system \| python on fedora	34s
check system \| python on opensuse	34s
check system \| pypy on ubuntu	48s
check system \| pyston	3m 50s
check system \| python on rocky linux 8	33s
check system \| python on rocky linux 9	26s
check system \| python on ubuntu	15s
check system \| alpine	22s
check system \| amazonlinux	25s
check system \| python via pyenv	1m 52s
check system \| python on macos aarch64	35s
check cache \| macos aarch64	13s
check system \| homebrew python on macos aarch64	25s
check system \| python on macos x86_64	23s
check system \| python3.13 on windows	1m 24s
check system \| python3.12 via chocolatey	2m 4s
check system \| conda3.8 on linux	1m 19s
check system \| embedded python3.10 on windows	34s
check system \| conda3.11 on linux	37s
check system \| python3.10 on windows	43s
check system \| conda3.8 on windows	1m 49s
check system \| conda3.11 on windows	1m 58s
check system \| python3.10 on windows x86	55s
check system \| conda3.8 on macos	48s
check system \| conda3.11 on macos	56s
	56m 29s

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