Fix workflows installing nightly IREE packages to use --pre.

[ScottTodd]

Pip will only install "pre-release" versions if --pre is set or the version is set explicitly: https://pip.pypa.io/en/stable/cli/pip_install/#pre-release-versions. The rc part of our rcYYYYMMDD suffix used in the nightly IREE packages is considered a "Pre-release segment" in the version string: https://packaging.python.org/en/latest/specifications/version-specifiers/#public-version-identifiers.

This should change workflow jobs like https://github.com/nod-ai/SHARK-Platform/actions/runs/11827078971/job/32954462017#step:5:163 that have been downloading iree-base-compiler-2.9.0 iree-base-runtime-2.9.0 to downloading the latest nightly versions instead, as they intend:

SHARK-Platform/.github/workflows/ci-sharktank.yml

Lines 64 to 67 in 51cf2f4

	# Update to the latest iree packages.
	pip install -f https://iree.dev/pip-release-links.html --upgrade \
	iree-base-compiler iree-base-runtime --src deps \
	-e "git+https://github.com/iree-org/iree-turbine.git#egg=iree-turbine"

[marbre]

Thanks for fixing this Scott! Tested locally.