Why is the F# version of this program 6x faster than the Haskell one?

If you switch to ByteString and stick with plain Haskell lists (instead of vectors) you will get a more efficient solution. You may also rewrite the solve function with a single left fold and bypass zip and right scan ⁽¹⁾.
Overall, on my machine, I get 20 times performance improvement compared to your Haskell solution ⁽²⁾.

Below Haskell code performs faster than the F# code:

import Data.List (unfoldr)
import Control.Applicative ((<$>))
import Control.Monad (replicateM_)
import Data.ByteString (ByteString)
import qualified Data.ByteString as B
import qualified Data.ByteString.Char8 as C

parse :: ByteString -> [Int]
parse = unfoldr $ C.readInt . C.dropWhile (== ' ')

solve :: [Int] -> Int
solve xs = foldl go (const 0) xs minBound
    where go f x s = if s < x then f x else s - x + f s

main = do
    [n] <- parse <$> B.getLine
    replicateM_ n $ B.getLine >> B.getLine >>= print . solve . parse

<sub>1. See edits for an earlier version of this answer which implements solve using zip and scanr.
2. HackerRank website shows even a larger performance improvement.</sub>