CI: Disable fail-fast for Ubuntu builds

[Warchamp7]

Description

Disables fail-fast for the Ubuntu build workflow.

Motivation and Context

Want Ubuntu 26.04 build to run still even if Ubuntu 24.04 fails.

How Has This Been Tested?

It has not yet.

Types of changes

• Tweak (non-breaking change to improve existing functionality)

Checklist:

• I have read the contributing document.
• My code has been run through clang-format.
• My code follows the project's style guidelines
• My code is not on the master branch.
• My code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[RytoEX]

Seems fine. We could use continue-on-error to make Ubuntu 26 continue if Ubuntu 24 fails, but stop Ubuntu 24 if Ubuntu 26 fails, but I'm not sure that's worth the added complexity, so this should be fine as-is.