diffoscope fails: try using --max-diff-block-lines-saved 100

This is the only option in the man page that mentions impact in memory
usage:

    --max-diff-block-lines-saved LINES

	Maximum number of lines saved per diff block. Most users should
        not need this, unless you run out of memory. This truncates diff(1)
        output before emitting it in a report, and affects all types of
        output, including --text and --json. (0 to disable, default: 0)