Add missing import in tests

board-shared/src/lexer.rs

@@ -68,6 +68,7 @@ pub fn lexer(input: &[Tile]) -> Result<Vec<Token>, ()> {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::tile::Digit;
 
     #[test]
     fn test_lex() {