python: Don't assume py2_runtime toolchain attribute exists.

There's a test that purposefully omits the attribute to test error messages.
To fix, just guard the access with hasattr().

Work towards #15897

PiperOrigin-RevId: 505715279
Change-Id: I4c8fe51783ac4f07e9c8ce32f457a65d941bf6b0

src/main/starlark/builtins_bzl/common/python/py_executable.bzl

@@ -308,7 +308,12 @@ def _maybe_get_runtime_from_ctx(ctx):
         # --python_path. See tools/python/toolchain.bzl.
         # TODO(#7844): Remove this hack when the autodetecting toolchain has a
         # Windows implementation.
-        if toolchain.py2_runtime and toolchain.py2_runtime.interpreter_path == "/_magic_pyruntime_sentinel_do_not_use":
+        if (
+            # BazelPyBinaryConfiguredTargetTest.toolchainInfoFieldHasBadVersion purposefully
+            # omits the py2_runtime attribute to test for other error messages.
+            hasattr(toolchain, "py2_runtime") and toolchain.py2_runtime and
+            toolchain.py2_runtime.interpreter_path == "/_magic_pyruntime_sentinel_do_not_use"
+        ):
             return None, None
 
         if not hasattr(toolchain, "py3_runtime"):