exercises(queen-attack): example: fix for Zig 0.12.0-dev (#368)

Resolve this error, which occured with the latest Zig master release:

    $ zig version
    0.12.0-dev.2341+92211135f
    $ 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

exercises/practice/queen-attack/.meta/example.zig

@@ -1,5 +1,4 @@
 const std = @import("std");
-const math = std.math;
 
 pub const QueenError = error{
     InitializationFailure,
@@ -24,8 +23,8 @@ pub const Queen = struct {
         if (self.row == other.row and self.col == other.col) {
             return QueenError.InvalidAttack;
         }
-        return (self.row == other.row) or (self.col == other.col) or
-            (math.absInt(self.row - other.row) catch unreachable ==
-            math.absInt(self.col - other.col) catch unreachable);
+        const row_diff = self.row - other.row;
+        const col_diff = self.col - other.col;
+        return (row_diff == 0) or (col_diff == 0) or (row_diff == col_diff) or (row_diff == -col_diff);
     }
 };