[FIX] stock: typo in unit of measure

before this commit, there is typo in unit of measure

after this commit, the typo will be corrected and
unity of measure will be updated to unit of measure

closes odoo/odoo#116699

X-original-commit: 11b89fcf
Signed-off-by: William Henrotin (whe) <whe@odoo.com>