Fix warnings from newer rust compiler which will be hard errors in Rust 2021
Fix warnings from newer rust compiler which will be hard errors in Rust 2021

Specifically fix the following warnings:

```console
warning: panic message is not a string literal
   --> tests\unit_tests.rs:760:30
    |
760 |             Err(e) => panic!(e),
    |                              ^
    |
    = note: this is no longer accepted in Rust 2021
help: add a "{}" format string to Display the message
    |
760 |             Err(e) => panic!("{}", e),
    |                              ^^^^^
help: or use std::panic::panic_any instead
    |
760 |             Err(e) => std::panic::panic_any(e),
    |                       ^^^^^^^^^^^^^^^^^^^^^
```

tafia/quick-xml,tafia/quick-xml