Replace `exec_tools` with `tools` in bazel genrule. (#77510)

As of the Bazel 6.x series, there is no difference between the
`exec_tools` and `tools`. Bazel 7 removes the `exec_tools` attribute
entirely. This commit updates to use the cannonical attribute name to
allow building `clang-tidy``with bazel 7.0.0, though it does not change
the default bazel version which remains at 6.1.2.

See also https://github.com/bazelbuild/bazel/issues/19132 for more
information.