[IMP] mass_mailing: move test tours to the test bundle

Before this commit, the moved tours were added to the common and
frontend bundles, and were thus loaded all the time even though
they only exist for testing purposes.

This commit moves the two files to the correct bundle.

closes odoo/odoo#121408

Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>

addons/mass_mailing/__manifest__.py

@@ -131,6 +131,9 @@
         'web.assets_frontend': [
             'mass_mailing/static/src/js/tours/**/*',
         ],
+        'web.assets_tests': [
+            'mass_mailing/static/tests/tours/**/*',
+        ],
         'web.qunit_suite_tests': [
             'mass_mailing/static/tests/mass_mailing_favourite_filter_tests.js',
             'mass_mailing/static/src/js/mass_mailing_snippets.js',