Use a byte-string literal in the genetic-code test (fix CI clippy)

The current stable clippy flags `[b'A', b'T', b'C', b'G']` with the
byte-str lint (can be written as `b"ATCG"`); under CI's -D warnings this
failed the clippy gate. Switch to the byte-string literal; no behaviour
change.

Author: Paururo

src/genetic_code.rs

@@ -208,10 +208,10 @@ mod tests {
         // Tables 1 and 11 should produce identical results for all 64 codons.
         let t1 = GeneticCode::new(1).unwrap();
         let t11 = GeneticCode::new(11).unwrap();
-        let bases = [b'A', b'T', b'C', b'G'];
-        for &a in &bases {
-            for &b in &bases {
-                for &c in &bases {
+        let bases = b"ATCG";
+        for &a in bases {
+            for &b in bases {
+                for &c in bases {
                     let codon = [a, b, c];
                     assert_eq!(
                         t1.translate(&codon),