[FIX] project: random cache flushing issue in test_task_portal_no_read

test_task_postal_no_read` calls `assertEqual`, which internally
creates a savepoint which flushes pending computations.

This is done by flushing the transaction (through the cursor), which
in turn goes and flushes the models.

The environment being used to flush the models is arbitrary, picked
from the set of all living environments associated with the
transaction favoring those with a user set. This means the environment
used to perform the pending computation can be a lot more restrictive
than the operation used to initiate said computation, which may lead
to the computation being flushed not being *possible to perform*.

The issue here is that the test specifically involves a restricted
user ("Portal user", created for the occasion). Logging the set, at
the start of the test function there are 11 active environments
associated with the superuser (uid1) and one (1) environment
associated with that user, let's call it 19 (because that's the uid it
gets when running only that job).

On the runbot the envset seems to shuffle really well and about 2/10
of the runs will have the env(uid=19) in leading position[0], thus try
to flush the *creation of the task* with the portal user, which
specifically does not have access to tasks.

This works around the issue by flushing the task creation in the
`setUp`, however the underlying issues remain.

[0]: This also seems to require some load on the runbots, if the
     runbots are pretty much unloaded (no pending builds)
     reproduction is never achieved. It is not clear why load
     would matter.

     Local reproduction was not successful, even using a dump from the
     runbot and inducing artificial load (via stress-ng).

closes odoo/odoo#87512

X-original-commit: fc08ff42ec8886f6258bde6586c4293b64c89456
Signed-off-by: Raphael Collet <rco@odoo.com>
Signed-off-by: Xavier Morel (xmo) <xmo@odoo.com>

addons/project/tests/test_access_rights.py

@@ -116,6 +116,7 @@ class TestCRUDVisibilityPortal(TestAccessRights):
     def setUp(self):
         super().setUp()
         self.project_pigs.privacy_visibility = 'portal'
+        self.env['base'].flush()
 
     @users('Portal user')
     def test_task_portal_no_read(self):