Fix benchmark regression in `pallet_elections_phragmen`

[ggwpez]

Somehow elections phragmen benchmark fails with Invalid input: UnableToPayBond discovered in paritytech/polkadot#5207.

@kianenigma noted that it is probably similar to what was fixed here #11057

somewhere I am using a bad value for the deposit
that error can arise every time there's a vote transaction, would be helpful if you look into the full backtrace of the falirure as well