[oui-flags] - svg published are invalid

[antleblanc]

Description

From the Storybook we list some flags available:
https://ovh.github.io/ovh-ui-kit/?path=/story/design-system-content-icons--flags

Using a given flags (:belgium: for instance) is not allowed due to invalid SVG format published to the registry.

Steps to reproduce

1. Use following code snippet

<span class="oui-flag oui-flag_be"></span>

2. See errors

Expected behavior:

SVG code from a given flag must be valid.

Actual behavior:

SVG code from a given flag is invalid.

Frequency:
5

Additional information

Issue appears since version v4.0.5.