♻️ Use Integer.try_convert (new in ruby 3.1+)

Now that the minimum ruby version is v3.1.0, we can use
Integer.try_convert.

lib/net/imap/sequence_set.rb

@@ -1284,8 +1284,7 @@ def input_to_tuples(obj)
       # String, Set, Array, or... any type of object.
       def input_try_convert(input)
         SequenceSet.try_convert(input) ||
-          # Integer.try_convert(input) || # ruby 3.1+
-          input.respond_to?(:to_int) && Integer(input.to_int) ||
+          Integer.try_convert(input) ||
           String.try_convert(input) ||
           input
       end