[CI] Lower code coverage target threshold to 80 or 90%

[rpreen]

I think having a target threshold of 100% code coverage is unrealistic and incentivises writing tests purely for code coverage rather than testing behaviour, which will lead to more work and more maintenance. Tests here should focus on real statistical scenarios rather than unit testing everything to 100%.

[JessUWE]

I agree - it’s unrealistic to aim for 100%, and it’s quite demanding. The code coverage rule should be updated so that when it reaches the benchmark of, say, 90%, it’s considered a pass rather than a fail. Setting the requirement at 100% makes contributors feel obligated to achieve that target as if it’s a strict rule, which isn’t a good practice. It can lead to unnecessary tests being added just to make the coverage pass.