fixed error message for one of the test cases to match expected one

Author: Anirav Kareddy

src/test/java/software/amazon/encryption/s3/S3EncryptionClientReEncryptInstructionFileTest.java

@@ -275,7 +275,7 @@ public void testAesReEncryptInstructionFileRejectsCustomInstructionFileSuffix()
         e
           .getMessage()
           .contains(
-            "Custom Instruction file suffix is not applicable for AES keyring!"
+            "Custom Instruction file suffix is only applicable for RSA keyring!"
           )
       );
     }