Load py_runtime_pair from rules_python for Bazel 8.

As suggested by @justinwon777 in #20335

PiperOrigin-RevId: 757604699

Author: haberman

python/dist/system_python.bzl

@@ -71,7 +71,7 @@ def fuzzing_py_install_deps():
 _build_file = """
 load("@bazel_skylib//lib:selects.bzl", "selects")
 load("@bazel_skylib//rules:common_settings.bzl", "string_flag")
-load("@bazel_tools//tools/python:toolchain.bzl", "py_runtime_pair")
+load("@rules_python//python:py_runtime_pair.bzl", "py_runtime_pair")
 
 cc_library(
    name = "python_headers",