style: include SPP_TOSTRING_ON_STRING (#5183)

Author: vil02

spotbugs-exclude.xml

@@ -261,9 +261,6 @@
     <Match>
         <Bug pattern="SLS_SUSPICIOUS_LOOP_SEARCH" />
     </Match>
-    <Match>
-        <Bug pattern="SPP_TOSTRING_ON_STRING" />
-    </Match>
     <!-- find-sec-bugs -->
     <Match>
         <Bug pattern="PREDICTABLE_RANDOM" />

src/main/java/com/thealgorithms/ciphers/DES.java

@@ -238,7 +238,7 @@ public String decrypt(String message) {
         }
         for (i = 0; i < l; i += 64) {
             String block = message.substring(i, i + 64);
-            String result = decryptBlock(block.toString(), subKeys);
+            String result = decryptBlock(block, subKeys);
             byte[] res = new byte[8];
             for (j = 0; j < 64; j += 8) {
                 res[j / 8] = (byte) Integer.parseInt(result.substring(j, j + 8), 2);