Update dependency com_github_grpc_grpc to v1.68.1

Author: renovate[bot]

bazel/zetasql_deps_step_2.bzl

@@ -275,9 +275,9 @@ py_library(
         if not native.existing_rule("com_github_grpc_grpc"):
             http_archive(
                 name = "com_github_grpc_grpc",
-                urls = ["https://github.com/grpc/grpc/archive/v1.43.2.tar.gz"],
-                sha256 = "b74ce7d26fe187970d1d8e2c06a5d3391122f7bc1fdce569aff5e435fb8fe780",
-                strip_prefix = "grpc-1.43.2",
+                urls = ["https://github.com/grpc/grpc/archive/v1.68.1.tar.gz"],
+                sha256 = "c8bb8a695208a15f6176146534b42b84806f3080ddd29fe89128a32ed943634b",
+                strip_prefix = "grpc-1.68.1",
             )
 
     if analyzer_deps: