[FIX] base: cannot specify 24-hour clock format and meridian

- Settings > manage languages > english > Set time format to `%H:%M:%S %p`
> Save
- Install Planning app > go to list view > Try modifying a time manually
(without using the widget which pops up).

Issue:
When trying to save the new time, an error pops up: `Can't include meridiem
when specifying 24-hour format`.

While parsing the new date, the `luxon` library throws this error to
prevent wrong hour values, such as `17 AM`.

Fix:
Prevent the user from inputting both `%H` and `%p` in the same time format
and display a warning notification.

opw-3038797

closes odoo/odoo#106846

Signed-off-by: Xavier Morel (xmo) <xmo@odoo.com>