Upgrade gradle version due to CVE

[manuelValch]

• I have searched the existing issues

Description

Fast-DDS-Gen is currently using gradle version 7.6 for build.

This version is affected by 3 major CVE which is a risk for the build machine / server:

• cve-2021-26291
• cve-2022-1471
• cve-2023-26053

So as a develloper I would like to update gradle version using the official documentation:
https://docs.gradle.org/current/userguide/upgrading_major_version_9.html

So that no more CVE when building fast-DDS-Gen from sources.

[manuelValch]

Update

Tried to scan with the same tool fastddsgen-4.0.4 (which uses same build-chain), no CVE detected so the incriminated packages are mostly used for building the app and not packaged whithin it (I guess).