Log Message:
devel/git-branchless: update to 0.8.0

v0.8.0: build: delete git-branchless-testing crate

 The git-branchless-lib crate has a dev-dependency on git-branchless-testing,
 and git-branchless-testing has a dependency on git-branchless-lib, inducing
 a circular dependency that means they can't be published to crates.io.
 This commit collapses them into the same crate again to resolve this circular
 dependency.