libjack2: fix source url

c733f0bf8a switched JACK to using overlay-style
mkDerivation, but forgot to change a reference to `version` to `finalAttrs.version`.

This wasn't caught at eval time because `with lib` was used, making the
source derivation try to fetch (at the time of writing) tag "23.05pre-git",
which obviously doesn't exist :D

Thanks to V for catching this [0].

[0]: https://github.com/NixOS/nixpkgs/pull/216096#issuecomment-1437763295

pkgs/misc/jackaudio/default.nix

@@ -34,7 +34,7 @@ stdenv.mkDerivation (finalAttrs: {
   src = fetchFromGitHub {
     owner = "jackaudio";
     repo = "jack2";
-    rev = "v${version}";
+    rev = "v${finalAttrs.version}";
     sha256 = "01s8i64qczxqawgrzrw19asaqmcspf5l2h3203xzg56wnnhhzcw7";
   };