Failing mass_mailing unit tests on Odoo.sh 15 because of Pillow version

[hwangh95]

Impacted versions:
15.0

Steps to reproduce:
On any 15.0 environment on Odoo.sh, install and run the unit tests for mass_mailing

Current behavior:
Fails as it trys to access ImageDraw.textbbox

Expected behavior:
Passing unit tests on base installation.

When I check pip list I see that Pillow is 7.0.0, which I'm guessing is because of

odoo/requirements.txt

Line 24 in 6b6536b

Pillow==9.0.1 # min version = 7.0.0 (Focal with security backports)

but as of #159994, it needs to be 8.0.0 minimum.

Error Logs:

Traceback (most recent call last):
  File "/home/odoo/src/odoo/odoo/addons/base/models/ir_http.py", line 242, in _dispatch
    result = request.dispatch()
  File "/home/odoo/src/odoo/odoo/http.py", line 819, in dispatch
    r = self._call_function(**self.params)
  File "/home/odoo/src/odoo/odoo/http.py", line 368, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/home/odoo/src/odoo/odoo/service/model.py", line 94, in wrapper
    return f(dbname, *args, **kwargs)
  File "/home/odoo/src/odoo/odoo/http.py", line 357, in checked_call
    result = self.endpoint(*a, **kw)
  File "/home/odoo/src/odoo/odoo/http.py", line 925, in __call__
    return self.method(*args, **kw)
  File "/home/odoo/src/odoo/odoo/http.py", line 546, in response_wrap
    response = f(*args, **kw)
  File "/home/odoo/src/odoo/addons/web_editor/controllers/main.py", line 127, in export_icon_to_png
    box = draw.textbbox((0, 0), icon, font=font_obj)
Exception

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/werkzeug/serving.py", line 306, in run_wsgi
    execute(self.server.app)
  File "/usr/lib/python3/dist-packages/werkzeug/serving.py", line 294, in execute
    application_iter = app(environ, start_response)
  File "/home/odoo/src/odoo/odoo/service/server.py", line 482, in app
    return self.app(e, s)
  File "/home/odoo/src/odoo/odoo/service/wsgi_server.py", line 112, in application
    return application_unproxied(environ, start_response)
  File "/home/odoo/src/odoo/odoo/service/wsgi_server.py", line 87, in application_unproxied
    result = odoo.http.root(environ, start_response)
  File "/home/odoo/src/odoo/odoo/http.py", line 1355, in __call__
    return self.dispatch(environ, start_response)
  File "/home/odoo/src/odoo/odoo/http.py", line 1321, in __call__
    return self.app(environ, start_wrapped)
  File "/usr/lib/python3/dist-packages/werkzeug/middleware/shared_data.py", line 220, in __call__
    return self.app(environ, start_response)
  File "/home/odoo/src/odoo/odoo/http.py", line 1548, in dispatch
    result = ir_http._dispatch()
  File "/home/odoo/src/odoo/addons/auth_signup/models/ir_http.py", line 19, in _dispatch
    return super(Http, cls)._dispatch()
  File "/home/odoo/src/odoo/addons/web_editor/models/ir_http.py", line 21, in _dispatch
    return super(IrHttp, cls)._dispatch()
  File "/home/odoo/src/odoo/addons/utm/models/ir_http.py", line 29, in _dispatch
    response = super(IrHttp, cls)._dispatch()
  File "/home/odoo/src/odoo/addons/http_routing/models/ir_http.py", line 519, in _dispatch
    result = super(IrHttp, cls)._dispatch()
  File "/home/odoo/src/odoo/odoo/addons/base/models/ir_http.py", line 246, in _dispatch
    return cls._handle_exception(e)
  File "/home/odoo/src/odoo/addons/utm/models/ir_http.py", line 34, in _handle_exception
    response = super(IrHttp, cls)._handle_exception(exc)
  File "/home/odoo/src/odoo/addons/http_routing/models/ir_http.py", line 616, in _handle_exception
    return super(IrHttp, cls)._handle_exception(exception)
  File "/home/odoo/src/odoo/odoo/addons/base/models/ir_http.py", line 214, in _handle_exception
    return request._handle_exception(exception)
  File "/home/odoo/src/odoo/odoo/http.py", line 763, in _handle_exception
    return super(HttpRequest, self)._handle_exception(exception)
  File "/home/odoo/src/odoo/odoo/http.py", line 301, in _handle_exception
    raise exception.with_traceback(None) from new_cause
AttributeError: 'ImageDraw' object has no attribute 'textbbox'