Actually run FEDemo tests

[thetic]

Description

Many FEDemo tests weren't run because they are intended to fail.
That's what EXPECT_FAIL_TEST is for.

Related Issues

Fixes # (issue number)

Type of Change

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Manual Verification (Optional)

If you have verified this change on hardware or a simulator not covered by CI (e.g., a specific ARM target), please describe it here:

• Target:
• Result:

Checklist

• I have written/updated documentation in docs/ for any user-facing changes.
• My code follows the project's naming conventions (mu::tiny namespace, INCLUDED_MUTINY_ guards, mutiny_ C-prefix).
• For new features, I have considered if a C-interface adapter (.h and .c.cpp) is required for parity.
• I have reviewed the CONTRIBUTING.md file to ensure compliance with architectural guidelines.

[coveralls]

coverage: 98.971%. remained the same
when pulling feb2578 on float-fail
into 1e7728b on main.