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

[Nick Desaulniers via llvm-commits]

nickdesaulniers wrote:

build is still red, now due to 9a9c1d4 and 9735873009ca86b03c3283d06edd1b3a190d4af9. Am I also on the hook to fix those? :^)

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