[rules_python] Mark internal_config_repo.bzl as public

Our linter needs to read this file in order to compare it to our vendored copy.

--- python/private/BUILD.bazel
+++ python/private/BUILD.bazel
@@ -80,4 +80,5 @@
     srcs = ["internal_config_repo.bzl"],
     deps = [":bzlmod_enabled_bzl"],
+    visibility = ["//visibility:public"],
 )
 
