Fix tests parameters & MAIL_DEBUG as integer

[nledez]

Problem
Flask-mail want a integer for MAIL_DEBUG parameter.

err: Traceback (most recent call last):
err:   File "/opt/zou/zouenv/bin/zou", line 5, in <module>
err:     from zou.cli import cli
err:   File "/opt/zou/zouenv/lib/python3.12/site-packages/zou/cli.py", line 11, in <module>
err:     from zou.app.utils import dbhelpers, auth, commands
err:   File "/opt/zou/zouenv/lib/python3.12/site-packages/zou/app/__init__.py", line 26, in <module>
err:     from zou.app import config, swagger
err:   File "/opt/zou/zouenv/lib/python3.12/site-packages/zou/app/config.py", line 84, in <module>
err:     MAIL_DEBUG = envtobool("MAIL_DEBUG", 0)
err:                  ^^^^^^^^^^^^^^^^^^^^^^^^^^
err:   File "/opt/zou/zouenv/lib/python3.12/site-packages/zou/app/utils/env.py", line 11, in envtobool
err:     return strtobool(os.getenv(key, default))
err:            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
err:   File "/opt/zou/zouenv/lib/python3.12/site-packages/zou/app/utils/string.py", line 9, in strtobool
err:     elif val.lower() in ("y", "yes", "t", "true", "on", "1"):
err:          ^^^^^^^^^
err: AttributeError: 'int' object has no attribute 'lower'
[202](https://github.com/cgwire/zou/actions/runs/11405086536/job/31735727254#step:3:203)4/10/18 13:56:40 Process exited with status 1

Solution
Correction of the conversion of the bool parameter to int.
The test parameters have also been modified to have the same behaviour as before.