Use Bazel 8

[veblush]

This turned out that we cannot upgrade Bazel to 8 until Tensorflow supports it. It fails with the following error

$ bazel build  tensorflow/lite/micro/...
WARNING: WORKSPACE support will be removed in Bazel 9 (late 2025), please migrate to Bzlmod, see https://bazel.build/external/migration.
ERROR: Traceback (most recent call last):
        File "/usr/local/google/home/veblush/.cache/bazel/_bazel_veblush/d9fcdcf3bc1994231b91aafb70b5034e/external/tensorflow_cc_deps/BUILD", line 7, column 16, in <toplevel>
                hdrs = glob(["_site/tensorflow/include/**"], allow_empty=False, exclude_directories=1),
Error in glob: glob pattern '_site/tensorflow/include/**' didn't match anything, but allow_empty is set to False (the default value of allow_empty can be set with --incompatible_disallow_empty_glob).
ERROR: /usr/local/google/home/veblush/.cache/bazel/_bazel_veblush/d9fcdcf3bc1994231b91aafb70b5034e/external/tensorflow_cc_deps/BUILD: no such target '@@tensorflow_cc_deps//:cc_library': target 'cc_library' not declared in package '' defined by /usr/local/google/home/veblush/.cache/bazel/_bazel_veblush/d9fcdcf3bc1994231b91aafb70b5034e/external/tensorflow_cc_deps/BUILD
ERROR: /usr/local/google/home/veblush/git/tflite-micro/python/tflite_micro/signal/BUILD:53:23: no such target '@@tensorflow_cc_deps//:cc_library': target 'cc_library' not declared in package '' defined by /usr/local/google/home/veblush/.cache/bazel/_bazel_veblush/d9fcdcf3bc1994231b91aafb70b5034e/external/tensorflow_cc_deps/BUILD and referenced by '//python/tflite_micro/signal:ops/_delay_op.so'
Target //tensorflow/lite/micro/kernels:decompress_test was skipped
ERROR: Analysis of target '//tensorflow/lite/micro/examples/micro_speech:audio_preprocessor' failed; build aborted: Analysis failed

BUG=N/A