Do not panic if the fdlimit call to increase the file descriptor limit fails (#2155)

# Description

Sometimes changing file descriptor limits is not allowed, but there is
no need to crash the node if/when this happens. Since `fdlimit`'s author
decided to use panics instead of returning `Result`, we need to catch
it.

# Checklist

- [x] My PR includes a detailed description as outlined in the
"Description" section above
- [ ] My PR follows the [labeling requirements](CONTRIBUTING.md#Process)
of this project (at minimum one label for `T`
  required)
- [ ] I have made corresponding changes to the documentation (if
applicable)
- [ ] I have added tests that prove my fix is effective or that my
feature works (if applicable)

---------

Co-authored-by: Koute <koute@users.noreply.github.com>

substrate/client/service/test/src/lib.rs

@@ -285,7 +285,7 @@ where
 		base_port: u16,
 	) -> TestNet<G, E, F, U> {
 		sp_tracing::try_init_simple();
-		fdlimit::raise_fd_limit();
+		fdlimit::raise_fd_limit().unwrap();
 		let runtime = Runtime::new().expect("Error creating tokio runtime");
 		let mut net = TestNet {
 			runtime,