aria2's OpenSSL integration breaks down when interacting with TLS v1.3
enabled websites which manifests in errors like these:
```
07/05 12:26:53 [NOTICE] Downloading 1 item(s)
07/05 12:26:54 [ERROR] CUID#7 - Download aborted. URI=https://catbox.moe
Exception: [AbstractCommand.cc:351] errorCode=1 URI=https://catbox.moe
-> [SocketCore.cc:1018] errorCode=1 SSL/TLS handshake failure: protocol error
```
There are multiple instances[1] of users reporting this to the aria2 issue
tracker, and one of those issues[2] documents using GnuTLS in place of OpenSSL
as a workaround for the TLS v1.3 woes. I've verified that it indeed fixes
the problem, and hence making this change in Nixpkgs.
1: https://github.com/aria2/aria2/issues?q=is%3Aissue+is%3Aopen+sort%3Aupdated-desc+%22protocol+error%22
2: https://github.com/aria2/aria2/issues/1494
29bd4a3af9