Update bazel build image for the driver

This is the same image used in grpc#388. It upgrades bazel from 6.1.2 to
6.4.0, which is the default supported version starting with v1.60.0.

Without this change, building the driver image fails with:

/tmp/build_output/5e0c6d2c26e81c9358486406038ccc44/external/com_google_protobuf/upb_generator/BUILD:266:21:
@com_google_protobuf//upb_generator:protoc-gen-upb_toolchain: no such attribute 'output_files' in 'proto_lang_toolchain' rule

https://github.com/grpc/grpc/blob/master/.bazelversion
https://github.com/grpc/grpc/blob/master/bazel/supported_versions.txt

containers/runtime/driver/Dockerfile

@@ -34,7 +34,7 @@ RUN git clone https://github.com/$REPOSITORY.git .
 RUN git checkout -f $GITREF
 
 # See https://github.com/grpc/grpc/blob/master/tools/dockerfile/README.md
-FROM us-docker.pkg.dev/grpc-testing/testing-images-public/bazel:0f909e43012a80faa92e07b7871268841ce56ebc@sha256:1118150d9d9479787165fff49f660a3dc633f1c57604305460172fc1916aa022
+FROM us-docker.pkg.dev/grpc-testing/testing-images-public/bazel:cacad91746cd598d8756de89b912be291de1f019@sha256:32bde2dcb2087f2a32afab59e4dfedf7e8c76a52c69881f63a239d311f0e5ecf
 
 COPY --from=0 /src/code /src/code
 RUN mkdir -p /tmp/build_output