internal(pystar): Only respect RULES_PYTHON_ENABLE_PYSTAR env var for…

… Bazel 7+

Respecting it for earlier versions was only done for testing purposes.
The implementation requires the `py_internal` object, which only exists
on Bazel 7 and higher.

Work towards bazelbuild#1069

python/private/internal_config_repo.bzl

@@ -58,18 +58,20 @@ bzl_library(
 """
 
 def _internal_config_repo_impl(rctx):
-    enable_pystar = _bool_from_environ(rctx, _ENABLE_PYSTAR_ENVVAR_NAME, _ENABLE_PYSTAR_DEFAULT)
+    pystar_requested = _bool_from_environ(rctx, _ENABLE_PYSTAR_ENVVAR_NAME, _ENABLE_PYSTAR_DEFAULT)
+
+    # Bazel 7+ (dev and later) has native.starlark_doc_extract, and thus the
+    # py_internal global, which are necessary for the pystar implementation.
+    if pystar_requested and hasattr(native, "starlark_doc_extract"):
+        enable_pystar = pystar_requested
+    else:
+        enable_pystar = False
+
     rctx.file("rules_python_config.bzl", _CONFIG_TEMPLATE.format(
         enable_pystar = enable_pystar,
     ))
 
-    if enable_pystar or (
-        # Bazel 7+ (dev and later) has native.starlark_doc_extract, and thus the py_internal global
-        hasattr(native, "starlark_doc_extract") and
-        # The logic to allow the symbol doesn't work properly under bzlmod,
-        # even if the symbol is otherwise functional.
-        not BZLMOD_ENABLED
-    ):
+    if enable_pystar:
         shim_content = _PY_INTERNAL_SHIM
         py_internal_dep = '"@rules_python//tools/build_defs/python/private:py_internal_renamed_bzl"'
     else: