Prepare 2.8.0rc1. (#13408)
Prepare 2.8.0rc1. (#13408)

[ci skip-rust]
[ci skip-build-wheels]
pantsbuild/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,pantsbuild/pants,benjyw/pants,pantsbuild/pants