As part of this PR https://github.com/openfoodfoundation/openfoodnetwork/pull/10329
LocalisedNumber validation was tightened, but that means negative number
were not valid anymore.
This commit has been cherry-picked after this fix has already been
applied. Now we just change the order of characters in the regex because
humans are used to reading the minus at the beginning of the number. But
this change doesn't change the logic at all.
