Update the Yum repositories used in the CI

Description

After the latest update of the AMC13 RPM packages, the CI was failing due to missing dependencies. Those dependencies are provided by the GCC8 version of uHAL/IPBus. This MR thus updates the Yum repositories to use their GCC8 version.

Taking the opportunity to also bump the CMSOS Worksuite release to version 15.18.0.3.

Please note that the gem904daq04 machine has already been updated to check whether the new repositories and libraries were fully functionnal.

How Has This Been Tested?

The CI passed and the xDAQ applications still run on the updated gem904daq04 machine.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.