fix f-string for 3.10

Author: dougbrn

tests/nested_pandas/nestedframe/test_nestedframe.py

@@ -1149,7 +1149,7 @@ def offset_avg(offset, col_to_avg, column_names):
     # Verify that we can understand a string argument to the map_rows function,
     # so long as it isn't a column name.
     def make_id(row, prefix_str):
-        return f"{prefix_str}{row["b"]}"
+        return f"{prefix_str}{row['b']}"
 
     result = nf.map_rows(make_id, columns="b", prefix_str="some_id_")
     assert result[0][1] == "some_id_4"