The "build_test" started failing to test anything a while back. For now, I've just modified our test process to build everything under //third_party directly.
Update the sha256 value for protobuf-java. The current value dates from verion 3.7.0 in cl/240867170 because we missed updating it in cl/572680710.
Make the test script use Bazelisk instead of trying to pick up Bazel from the user's environment (since users probably don't have the "right" version installed).
Add JSpecify, and unbreak some things:
RELNOTES=n/a