Bug 1864: Add new af-south-1 and eu-south-1 AWS regions

https://winscp.net/tracker/1864
(cherry picked from commit bf459f235d5c4eb6080c800f8cee7ad82804910f)

Source commit: 6b6bd19c4533a79940455109a004bd81b42fae96

source/forms/SiteAdvanced.dfm

@@ -1026,6 +1026,7 @@ object SiteAdvancedDialog: TSiteAdvancedDialog
             Text = 'S3DefaultRegionCombo'
             OnChange = DataChange
             Items.Strings = (
+              'af-south-1'
               'ap-east-1'
               'ap-northeast-1'
               'ap-northeast-2'
@@ -1038,6 +1039,7 @@ object SiteAdvancedDialog: TSiteAdvancedDialog
               'cn-northwest-1'
               'eu-central-1'
               'eu-north-1'
+              'eu-south-1'
               'eu-west-1'
               'eu-west-2'
               'eu-west-3'