Move protoc to 3.21 to match Tensorflow.

Also needed to r/EXPECT_OK/REVERB_EXPECT_OK. I am not sure what changed
or how it relates to protoc; but it needs to be in this CL for presubmit
to pass. This is also the pattern TensorFlow and reverb follow so it just
aligns the code to use `REVERB_EXPECT` vs `EXPECT` for `OK`

PiperOrigin-RevId: 506622456
Change-Id: I8c42fb72aa1705c2d98c25c31db2a92ffced838d

WORKSPACE

@@ -8,8 +8,8 @@ workspace(name = "reverb")
 #     curl -L "https://github.com/protocolbuffers/protobuf/releases/download/v${PROTOC_VERSION}/protoc-${PROTOC_VERSION}-linux-x86_64.zip" | sha256sum
 #  3. Update the two variables below.
 #
-PROTOC_VERSION = "3.9.0"
-PROTOC_SHA256 = "15e395b648a1a6dda8fd66868824a396e9d3e89bc2c8648e3b9ab9801bea5d55"
+PROTOC_VERSION = "21.0"
+PROTOC_SHA256 = "a2a92003da7b8c0c08aab530a3c1967d377c2777723482adb9d2eb38c87a9d5f"
 
 load(
     "//reverb/cc/platform/default:repo.bzl",

reverb/cc/ops/queue_writer_test.cc

@@ -486,7 +486,7 @@ TEST(QueueWriter, CreateItemWithSqueezedColumn) {
   auto status = writer.CreateItem(
       "table", 1.0,
       {TrajectoryColumn({step[0].value()}, true)});
-  EXPECT_OK(status);
+  REVERB_EXPECT_OK(status);
   EXPECT_EQ(queue.size(), 1);
 
   for (auto trajectory : queue){