argparse howto: Use f-string in preference to "...".format() (#98883)

Doc/howto/argparse.rst

@@ -761,9 +761,9 @@ your program, just in case they don't know::
    if args.quiet:
        print(answer)
    elif args.verbose:
-       print("{} to the power {} equals {}".format(args.x, args.y, answer))
+       print(f"{args.x} to the power {args.y} equals {answer}")
    else:
-       print("{}^{} == {}".format(args.x, args.y, answer))
+       print(f"{args.x}^{args.y} == {answer}")
 
 Note that slight difference in the usage text. Note the ``[-v | -q]``,
 which tells us that we can either use ``-v`` or ``-q``,