[llvm] [bazel] update .bazelversion to 8.0.0 (PR #119425)

[Nick Desaulniers via llvm-commits]

nickdesaulniers wrote:

looks like there's some build failures now: https://buildkite.com/llvm-project/upstream-bazel/builds/119358#0193b266-65c9-4ee4-8d53-5fde26020ff7

https://github.com/llvm/llvm-project/pull/119425