mdf2iso: fix src

Debian's anonscm is dead, they use a Gitlab instance now.

The hash changed because the branch was rebased upstream, the diff is
a noop.

pkgs/tools/cd-dvd/mdf2iso/default.nix

···
   version = "0.3.1";
 
   src = fetchgit {
-    url    = https://anonscm.debian.org/cgit/collab-maint/mdf2iso.git;
-    rev    = "5a8acaf3645bff863f9f16ea1d3632c312f01523";
-    sha256 = "0f2jx8dg1sxc8y0sisqhqsqg7pj1j84fp08nahp0lfcq522pqbhl";
+    url    = "https://salsa.debian.org/debian/mdf2iso";
+    rev    = "c6a5b588318d43bc8af986bbe48d0a06e92f4280";
+    sha256 = "0xg43jlvrk8adfjgbjir15nxwcj0nhz4gxpqx7jdfvhg0kwliq0n";
   };
 
   meta = with stdenv.lib; {