Fix UnexpectedImprovement(Pass) note message
The note in the Merge Request summarizing the expectation changes reports as possible regression (when it is not a flake) all the test results except the old UnexpectedPass. The management of the new UnexpectedImprovement(...) result wasn't properly set here and tagged UnexpectedImprovement(Pass) as a regression.
We can see an example in one of the recent uprev Piglit in Mesa
mesa/mesa!28820 (comment 2379492)
Possible regressions on ('radeonsi-stoney-gl:x86_64', 'amd'):
- spec@arb_gpu_shader_fp64@execution@conversion@frag-conversion-explicit-dvec3-vec3, UnexpectedImprovement(Pass)