The following would do the trick:

my @selection = @nums;
for (0..7) {
   my $i = $_ + rand(@selection - $_);
   ($selection[$_], $selection[$i]) = ($selection[$i], $selection[$_])
}

splice(@selection, 8);
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But it would be better (simpler, cleaner, faster) to just use List::Util's shuffle.

use List::Util qw( shuffle );

my @selection = (shuffle(@nums))[0..7];
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