atomic-swap: fix build

```
vendor/github.com/quic-go/quic-go/internal/qtls/go121.go:5:13: cannot use "The version of quic-go you're using can't be built on Go 1.21 yet. For more details, please see https://github.com/quic-go/quic-go/wiki/quic-go-and-Go-versions." (untyped string constant "The version of quic-go you're using can't be built on Go 1.21 yet. F...) as int value in variable declaration
```

Artturin f47e5cbf 58deb9e3

+3 -1
+3 -1
pkgs/applications/blockchains/atomic-swap/default.nix
··· 1 - { lib, buildGoModule, fetchFromGitHub, nix-update-script, makeWrapper, monero-cli }: 1 + { lib, buildGo120Module, fetchFromGitHub, nix-update-script, makeWrapper, monero-cli }: 2 + 2 3 let 3 4 pname = "atomic-swap"; 4 5 version = "0.4.2"; 6 + buildGoModule = buildGo120Module; 5 7 in 6 8 buildGoModule { 7 9 inherit pname version;