exercises(queen-attack): example: fix for Zig 0.12.0-dev

[ee7]

At the time of writing, Zig master supports every test file on the track. However, Zig master no longer supports some of the example solutions in this repo. Work towards that.

The track officially supports only Zig 0.11.0, but I'd like to support Zig master too when we can do that in a backwards-compatible way.

---

Resolve this error from the latest Zig master release:

$ zig version
0.12.0-dev.2063+804cee3b9
$ bin/run-tests queen-attack
Running tests for queen-attack...
queen_attack.zig:28:18: error: root struct of file 'math' has no member named 'absInt'
            (math.absInt(self.row - other.row) catch unreachable ==
             ~~~~^~~~~~~
/opt/zig/lib/std/math.zig:1:1: note: struct declared here
const builtin = @import("builtin");
^~~~~
referenced by:
    test.cannot attack if falling diagonals are only the same when reflected across the longest falling diagonal: test_queen_attack.zig:87:34
    remaining reference traces hidden; use '-freference-trace' to see all reference traces