fix: v3bwfile: Clarify percent warning

about the difference between the sum of the last consensus weight and
the sum of the reported weight in the just generated Bandwidth File.
Otherwise, when looking at the warnings only, it's not explained what
the percentage is about.

Closes #40115
10 jobs for m13_issue40115_weight_sum_difference in 9 minutes and 49 seconds (queued for 2 seconds)