Remove pinning protobuf version since 3.20.3 is old and not supported by Tensorflow

PiperOrigin-RevId: 728286886

Author: rtg0795

WORKSPACE

@@ -31,9 +31,9 @@ bind(
 
 http_archive(
     name = "com_google_protobuf",
-    sha256 = "f66073dee0bc159157b0bd7f502d7d1ee0bc76b3c1eac9836927511bdc4b3fc1",
-    strip_prefix = "protobuf-3.21.9",
-    urls = ["https://github.com/protocolbuffers/protobuf/archive/v3.21.9.zip"],
+    sha256 = "d5558cd419c8d46bdc958064cb97f963d1ea793866414c025906ec15033512ed",
+    strip_prefix = "protobuf-4.21.6",
+    urls = ["https://github.com/protocolbuffers/protobuf/archive/v4.21.6.zip"],
 )
 
 # ZLIB. Need by com_google_protobuf.

requirements.txt

@@ -8,7 +8,7 @@ scipy
 # with both new and old protobuf stubs. This is needed to resolve
 # Keras-TensorFlow circular dependency issue, when one of them gets a dependency
 # incompatible with another one (protobuf in this specific case).
-protobuf==3.20.3
+protobuf==4.21.6
 tf-nightly
 portpicker
 pyyaml