Use of newAV_alloc_x() was added in a7dffb8f (Add modperl support for
sasl, 2025-03-16), but it has the unintended consequence of increasing
the minimum Perl version a bit more than desired. Replace it with the
roughly equivalent code as documented in perlapi(1), which can be read
online at <https://perldoc.perl.org/perlapi#newAV>.
Fix#1966
