[FIX] test_lint: force absolute path to compute odoo path

When using the flamegraph module from a parent directory of odoo, the
dirname method returns a relative path, leading to a traceback.

With this commit, the odoo_path is enforced to be an absolute path.

closes odoo/odoo#40124

Signed-off-by: Christophe Monniez (moc) <moc@odoo.com>