Spec fix LocalisedNumber validation to allow negative number

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.

lib/spree/localized_number.rb

@@ -45,7 +45,7 @@ module Spree
     def self.valid_localizable_number?(number)
       return true unless number.is_a?(String) || number.respond_to?(:to_d)
       # Invalid if only two digits between dividers, or if any non-number characters
-      return false if number.to_s =~ /[.,]\d{2}[.,]/ || number.to_s =~ /[^0-9,.-]+/
+      return false if number.to_s =~ /[.,]\d{2}[.,]/ || number.to_s =~ /[^-0-9,.]+/
 
       true
     end

spec/lib/spree/localized_number_spec.rb

@@ -58,6 +58,12 @@ describe Spree::LocalizedNumber do
       it "returns true" do
         expect(described_class.valid_localizable_number?(1599.99)).to eql true
       end
+
+      context "with a negative number" do
+        it "returns true" do
+          expect(described_class.valid_localizable_number?(-1599.99)).to eql true
+        end
+      end
     end
 
     context "with letters" do