updated file io test to avoid crash

src/main.cpp

@@ -20,7 +20,7 @@ int main(int argc, char* argv[])
     amsstring4_test_strip();
     amsstring4_test_freadwrite();
 
-    amsstring4_test_concatenation_operators();
+    amsstring4_test_concatenation_operators(); //segfault on Debian11?
     
     return ret;
 }