Looks like test for Go solution isn't correct. Test matrix is equal to base matrix.

With matrix = [[3 1 7 7 7] [9 9 6 5 4] [9 9 5 7 4] [1 1 8 5 8] [2 9 7 4 7]]
Expected
<[][]int | len:5, cap:5>: [[7, 4, 4, 8, 7], [7, 5, 8, 1, 4], [7, 7, 5, 9, 7], [1, 5, 6, 9, 9], [3, 9, 9, 1, 2]]
to equal
<[][]int | len:5, cap:8>: [[3, 1, 7, 7, 7], [9, 9, 6, 5, 4], [9, 9, 5, 7, 4], [1, 1, 8, 5, 8], [2, 9, 7, 4, 7]]