[IMP] website: make website_nightly build work before 16.4

We have introduced a new tag `website_nightly` which is linked to a
custom build on the nightly.
It has been introduced with this commit [1].

The goal is to extract the `external` tagged tests linked to the website
app to another special build linked to the website team.
Otherwise, we would not see when the test fail, as the `external` build
of the nightly is always red and we don't check why all the time.

Encapsulating this in a new build and linking to our team means that
whenever the test fail in a nightly, we will be visually warned on the
runbot homepage by a red warning, see screenshot on the PR of this
commit.

Sadly, before 16.4, as there is not yet `website_nightly` tours, the
build is considered failed, showing the error.
Another solution would have been to somehow disable this tour on Odoo
versions < 16.4 but it we opted for this solution as:
- It's simpler, no need to add yet another custom stuff in runbot
- It will work out of the box should be introduce such a test in those
  versions: we won't need to ask runbot to activate the test in another
  version, should we even think about it..

[1]: https://github.com/odoo/odoo/commit/a0d0afb20594aa103eb1d0476d53012b9821e861



closes odoo/odoo#125847

X-original-commit: 2402ce27
Signed-off-by: Xavier Dollé (xdo) <xdo@odoo.com>
Signed-off-by: Romain Derie (rde) <rde@odoo.com>

addons/website/tests/test_views_inherit_module_update.py

 # -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
+from odoo.tests import HttpCase, standalone, tagged
+
+
+@tagged('website_nightly', '-standard')
+class TestWebsiteNightlyRunbot(HttpCase):
+    def test_01_website_nightly_runbot(self):
+        """ This test is just here to avoid runbot to raise an error on the
+        ``website_nightly`` build. Indeed, if not a single test with this tag is
+        found, the build will be considered as failed.
+        In Odoo 16.4 a real test is using this tag.
+        """
+
+
 """ This test ensure `inherit_id` update is correctly replicated on cow views.
 The view receiving the `inherit_id` update is either:
 1. in a module loaded before `website`. In that case, `website` code is not
@@ -13,8 +26,6 @@ The view receiving the `inherit_id` update is either:
    `test_specific_view_module_update_inherit_change` in `website` module.
 """
 
-from odoo.tests import standalone
-
 
 @standalone('cow_views_inherit', 'website_standalone')
 def test_01_cow_views_inherit_on_module_update(env):