Fix compatibility with rules_proto 7

Author: fmeum

protoc/private/prebuilt_protoc_toolchain.bzl

@@ -42,14 +42,15 @@ def _prebuilt_protoc_repo_impl(rctx):
     )
     build_content = """\
 # Generated by @rules_proto//proto/toolchains:prebuilt_protoc_toolchain.bzl
-load("@rules_proto//proto/private/rules:proto_toolchain_rule.bzl", "proto_toolchain")
 
-package(default_visibility=["//visibility:public"])
+# This is a workaround for proto_toolchain not allowing to set visibility.
+package(default_visibility = ["//visibility:public"])
+
+load("@rules_proto//proto:proto_toolchain.bzl", "proto_toolchain")
 
 proto_toolchain(
     name = "prebuilt_protoc_toolchain",
     proto_compiler = "{protoc_label}",
-    visibility = ["//visibility:public"],
 )
 """.format(
         protoc_label = ":bin/protoc.exe" if rctx.attr.platform.startswith("win") else ":bin/protoc",