[board] Fix a handful of linter warnings by allowing them

The linter also requires non-compliant formatting of the constants produced in
the coordinate_enum macro to be marked as allowed.

board/src/square.rs

@@ -51,6 +51,7 @@ macro_rules! coordinate_enum {
                     const $variant: usize = $name::$variant as usize;
                 )*
 
+                #[allow(non_upper_case_globals)]
                 match index {
                     $($variant => Some($name::$variant),)*
                     _ => None,