Add regression test for pylint-dev#8109

Author: Pierre-Sassoulas

tests/functional/r/regression_02/regression_8109.py

@@ -0,0 +1,13 @@
+
+# pylint: disable=missing-docstring
+
+
+from dataclasses import dataclass
+@dataclass
+class Number:
+    amount: int | float
+    round: int = 2
+
+    def __str__(self):
+        number_format = "{:,.%sf}" % self.round
+        return number_format.format(self.amount).rstrip("0").rstrip(".")