I hadn't tried it earlier, but I get the same here with 5.10.0, with & without warnings. It appears that Deprecated use of my() in false conditional applies only in limited cases:

my $x if 0;     #warns
my $x if "";    #warns
my $x if undef; #OK
my $x = 0 if 0; #OK
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Test program used:

use warnings;
sub a { my $x = 0 if undef;  print ++$x }
a for 1 .. 3;
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