Expose `--python` as an environment variable #5611

Job	Run time
build binary \| macos aarch64	1m 6s
build binary \| linux	2m 41s
build binary \| macos x86_64	1m 46s
build binary \| windows	1m 36s
cargo clippy \| ubuntu	42s
cargo test \| ubuntu	3m 57s
cargo fmt	21s
cargo test \| windows	6m 58s
cargo clippy \| windows	2m 35s
cargo test \| macos	4m 27s
check windows trampoline	4m 12s
check system \| homebrew python on macos aarch64	23s
check cache \| macos aarch64	11s
check system \| python on macos aarch64	18s
check system \| python3.10 on windows x86	48s
check system \| python3.10 on windows	48s
check system \| embedded python3.10 on windows	36s
check system \| python3.12 via chocolatey	1m 18s
check system \| python3.13 on windows	1m 8s
check system \| python on macos x86_64	38s
check system \| python on debian	45s
check system \| python on fedora	34s
check cache \| ubuntu	43s
ecosystem test \| prefecthq/prefect	1m 55s
ecosystem test \| pallets/flask	17s
check system \| alpine	1m 4s
check system \| conda3.8 on linux	44s
check system \| python on opensuse	36s
check system \| conda3.11 on linux	38s
check system \| python via pyenv	1m 51s
check system \| conda3.8 on windows	3m 14s
check system \| pypy on ubuntu	29s
check system \| pyston	4m 5s
check system \| conda3.11 on windows	1m 47s
check system \| conda3.8 on macos	41s
check system \| python on rocky linux 8	39s
check system \| python on ubuntu	24s
check system \| conda3.11 on macos	46s
check system \| python on rocky linux 9	24s
check system \| amazonlinux	31s
	58m 36s

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