Inconsistent country variation: Singapore

[baltpeter]

We've decided that Singapore should be written as "Republic of Singapore":

https://github.com/datenanfragen/data/blob/6aaea30760db9edd45979be0c0b6c437e4d2f01d/src/checks/record/end-address-in-country.ts#L5

But we also allow the native property from the countries-list library:

https://github.com/datenanfragen/data/blob/6aaea30760db9edd45979be0c0b6c437e4d2f01d/src/checks/record/end-address-in-country.ts#L16-L20

And that's "Singapore" in that case. We currently have records with both variations.