Set os.environ.setdefault when setting DJANGO_SETTINGS_MODULE
in wsgi.py so that other settings modules can be used by
setting DJANGO_SETTINGS_MODULE.

Upgrade dropbox dependency to 11.36.2 to avoid a dependency metadata issue.

Without this fix, `pip install -r requirements.txt` fails in pip >=24.1
with the following error:

```
WARNING: Ignoring version 11.36.0 of dropbox since it has invalid metadata:
Requested dropbox==11.36.0 from https://files.pythonhosted.org/packages/11/7e/e66327f3535cf5b58b3c152144744fc5727355357304facf61e43ab1b895/dropbox-11.36.0-py3-none-any.whl (from -r requirements.txt (line 46)) has invalid metadata: .* suffix can only be used with `==` or `!=` operators
    stone (>=2.*)
           ~~~~^
Please use pip<24.1 if you need to use this version.
```

Fixed in dropbox-sdk-python here:

dropbox/dropbox-sdk-python#456

Use os.environ.setdefault when setting DJANGO_SETTINGS_MODULE
in gmn_test_case.py so that other settings modules can be used by
setting DJANGO_SETTINGS_MODULE.

Upgrade dropbox to fix dependency metadata problem

…-module

Allow overrides of DJANGO_SETTINGS_MODULE in wsgi.py