games/anki: Unbreak after 2cf2d5e3e01fdbd2

The Bazel 4.2.0 release contains a change that handles the execution
of stub Python scripts differently. [1]

Remedy the issue for now by setting "stub_shebang", which was introduced
with Bazel 4.2.0, accordingly instead of using its default value.

[1] https://blog.bazel.build/2021/08/18/bazel-4.2.html#python