test: Adding notStrictEqual to setencoding test

This is changing a notEqual test to notStrictEqual
as reference in pr: #9997

Author: pauljlucas

test/parallel/test-tls-set-encoding.js

@@ -51,7 +51,7 @@ server.listen(0, function() {
 
     // Confirming the buffer string is encoded in ASCII
     // and thus does NOT match the UTF8 string
-    assert.notEqual(buffer, messageUtf8);
+    assert.notStrictEqual(buffer, messageUtf8);
 
     // Confirming the buffer string is encoded in ASCII
     // and thus does equal the ASCII string representation