Explicitly use Perl 5.32

Was already implicitly required (since 59387ddb) because RevBank::Amount
uses the "isa" feature, which was introduced in Perl 5.32 (but no longer
experimental since 5.36, not 5.32 as the old comment said).

Perl 5.32 was released in June 2020, and ships with Debian bullseye
("oldstable") which was released in August 2021.

t/amount.t

@@ -1,4 +1,4 @@
-use v5.28;
+use v5.32;
 use warnings;
 
 use Test::More;