lingo: use "an" before words starting with Ü

tests/test_lingo.py

@@ -0,0 +1,9 @@
+from pqcli.lingo import indefinite, to_roman
+
+
+def test_indefinite_article() -> None:
+    assert indefinite("Orc", 1) == "an Orc"
+    assert indefinite("Ürn", 1) == "an Ürn"
+    assert indefinite("über-Orc", 1) == "an über-Orc"
+    assert indefinite("?", 1) == "a ?"
+    assert indefinite("Rat", 1) == "a Rat"