[gdb/testsuite] Fix pi approximation

In gdb.dap/ada-non-ascii/prog.adb, I came across the following:
...
   π : Integer := 3;            --  The Indiana Approximation.
...

This article [1] explains the background behind the comment: the Indiana pi
bill.

Given that the common interpretation seems to be that the bill implies that
π == 3.2 [2]:
...
The bill ... has been claimed to imply a number of different values for π,
although the closest it comes to explicitly asserting one is the wording "the
ratio of the diameter and circumference is as five-fourths to four", which
would make π = 16⁄5 = 3.2, ... .
...
change the type to float, and set it to 3.2.

Luckily, in this particular case, changing the approximation of π has no
effect, so the test-case still passes :) .

Tested on x86_64-linux.

Approved-by: Kevin Buettner <kevinb@redhat.com>

[1] https://en.wikipedia.org/wiki/Indiana_pi_bill
[2] https://en.wikipedia.org/wiki/Approximations_of_pi#Indiana_bill