post_gen_project hook script fails upon attempting to create new extension

Even though I use the docker install, I get the exact same error as described in [this issue from someone who installed ckan from source](https://github.com/ckan/ckan/issues/8316):

```
Traceback (most recent call last):
File "/tmp/tmpqq3axb1k.py", line 88, in
"_checkout": null,
NameError: name 'null' is not defined
Stopping generation because post_gen_project hook script didn't exit successfully
Traceback (most recent call last):
File "/usr/local/bin/ckan", line 8, in
sys.exit(ckan())
File "/usr/local/lib/python3.10/site-packages/click/core.py", line 1157, in __call__
return self.main(*args, **kwargs)
File "/usr/local/lib/python3.10/site-packages/click/core.py", line 1078, in main
rv = self.invoke(ctx)
File "/usr/local/lib/python3.10/site-packages/click/core.py", line 1688, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/usr/local/lib/python3.10/site-packages/click/core.py", line 1688, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/usr/local/lib/python3.10/site-packages/click/core.py", line 1434, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/usr/local/lib/python3.10/site-packages/click/core.py", line 783, in invoke
return __callback(*args, **kwargs)
File "/srv/app/src/ckan/ckan/cli/generate.py", line 114, in extension
cookiecutter(template_loc, no_input=True, extra_context=context,
File "/usr/local/lib/python3.10/site-packages/cookiecutter/main.py", line 182, in cookiecutter
result = generate_files(
File "/usr/local/lib/python3.10/site-packages/cookiecutter/generate.py", line 419, in generate_files
run_hook_from_repo_dir(
File "/usr/local/lib/python3.10/site-packages/cookiecutter/hooks.py", line 157, in run_hook_from_repo_dir
run_hook(hook_name, project_dir, context)
File "/usr/local/lib/python3.10/site-packages/cookiecutter/hooks.py", line 140, in run_hook
run_script_with_context(script, project_dir, context)
File "/usr/local/lib/python3.10/site-packages/cookiecutter/hooks.py", line 123, in run_script_with_context
run_script(temp.name, cwd)
File "/usr/local/lib/python3.10/site-packages/cookiecutter/hooks.py", line 94, in run_script
raise FailedHookException(
cookiecutter.exceptions.FailedHookException: Hook script failed (exit status: 1)
```

According to [this commit](https://github.com/ckan/ckan/pull/8437), the Cookicutter 2.6 update caused a problem and it seems like that was fixed by [making some changes to post_gen_project.py](https://github.com/ckan/ckan/pull/8437/commits/665c235dfe411b64c71978d4ae5a4b1816f8979e), but when I build the containers and take a look inside, I get the pre-fix post_gen_project.py file with the whole 'context = {{ cookiecutter | jsonify }}' thing and if I manually alter that file according to the fix I can create a new extension without any problems. Is there something wrong on my end or was the fix just not adopted by ckan-docker?