Surprising Ruby benchmark results for Array#unshift: 2.5.9 vs 2.6.0

2.5.9-results.txt

Warming up --------------------------------------
       Array#unshift     1.000  i/100ms
          Array#push    16.000  i/100ms
Calculating -------------------------------------
       Array#unshift      0.428  (± 0.0%) i/s -      3.000  in   7.014513s
          Array#push    178.573  (± 9.0%) i/s -    896.000  in   5.064291s

Comparison:
          Array#push:      178.6 i/s
       Array#unshift:        0.4 i/s - 417.41x  (± 0.00) slower

2.6.0-results.txt

Warming up --------------------------------------
       Array#unshift    17.000  i/100ms
          Array#push    19.000  i/100ms
Calculating -------------------------------------
       Array#unshift    181.828  (± 6.6%) i/s -    918.000  in   5.076970s
          Array#push    187.124  (± 8.0%) i/s -    931.000  in   5.011387s

Comparison:
          Array#push:      187.1 i/s
       Array#unshift:      181.8 i/s - same-ish: difference falls within error

benchmark.rb

require 'benchmark/ips'

Benchmark.ips do |x|
  x.report('Array#unshift') do
    array = (1..100).to_a
    100_000.times { |i| array.unshift(i) }
  end

  x.report('Array#push') do
    array = (1..100).to_a
    100_000.times { |i| array.push(i) }
  end

  x.compare!
end