Update dependency com_google_protobuf to v21.12

Author: renovatebot-confluentinc[bot]

test_cross_build/WORKSPACE

@@ -31,9 +31,9 @@ http_archive(
 
 http_archive(
     name = "com_google_protobuf",
-    sha256 = "75be42bd736f4df6d702a0e4e4d30de9ee40eac024c4b845d17ae4cc831fe4ae",
-    strip_prefix = "protobuf-21.7",
-    url = "https://github.com/protocolbuffers/protobuf/archive/refs/tags/v21.7.tar.gz",
+    sha256 = "22fdaf641b31655d4b2297f9981fa5203b2866f8332d3c6333f6b0107bb320de",
+    strip_prefix = "protobuf-21.12",
+    url = "https://github.com/protocolbuffers/protobuf/archive/refs/tags/v21.12.tar.gz",
 )
 
 load("@rules_proto//proto:repositories.bzl", "rules_proto_dependencies")