CI tests: Use `! grep` to assert something is missing
    
    Previously, we have used `grep -v` to assert something is *not* there.
    However, that doesn't work. See for example this file:
    
        $ cat TEST
        line1
        line2
        line3
    
        $ grep -v line4 TEST
        line1
        line2
        line3
        $ echo $?
        0
    
    This gives a false sense of correctness, however it exits will 0 with anything:
    
        $ grep -v line3 TEST
        line1
        line2
        $ echo $?
        0
    
    Instead, we use `! grep` now:
    
        $ ! grep line4 TEST
        $ echo $?
        0
    
        $ ! grep line3 TEST
        line3
        $ echo $?
        1
    
    Additionally, remove a trailing slash from one of the checks to match both cases
    (with or without the slash).