Fix SHA-256 algorithm name to be more robust across JVM versions

Author: alextwoods

services/signin/src/main/java/software/amazon/awssdk/services/signin/internal/OnDiskTokenManager.java

@@ -54,7 +54,7 @@ private OnDiskTokenManager(Path cacheLocation, String loginSession) {
 
     private String deriveCacheKey(String loginSession) {
         try {
-            MessageDigest sha1 = MessageDigest.getInstance("sha256");
+            MessageDigest sha1 = MessageDigest.getInstance("SHA-256");
             sha1.update(loginSession.getBytes(StandardCharsets.UTF_8));
             return BinaryUtils.toHex(sha1.digest()).toLowerCase(Locale.ENGLISH);
         } catch (NoSuchAlgorithmException e) {