"guessed cause of the failure" should include the list of failed tests

[RalfJung]

rust-lang/rust#80394 (comment) is a pretty good guess of what to show for the failure, I just have one complaint: usually the thing that I care most about is the list of failed UI tests. Those are what I need to get over locally. Unfortunately, while the bot shows some text from before and after the list, it chose to cut out exactly that list:

error: aborting due to previous error

---

Some tests failed in compiletest suite=ui mode=ui host=x86_64-unknown-linux-gnu target=x86_64-unknown-linux-gnu

Original log:

error: aborting due to previous error


------------------------------------------



failures:
    [ui] ui/error-codes/E0396-fixed.rs

test result: FAILED. 11115 passed; 1 failed; 84 ignored; 0 measured; 0 filtered out; finished in 144.36s

Some tests failed in compiletest suite=ui mode=ui host=x86_64-unknown-linux-gnu target=x86_64-unknown-linux-gnu

I am not sure why the log chose to remove these few lines when it showed so many others, but in so doing it removed the lines I care about most. ;)