fetchzip: fix unpacking regression

This resolves a regression introduced in fc01353703, where providing a
name without a proper extension breaks existing uses of fetchzip (they
now fail to unpack). Of particular note, that commit broke all uses of
fetchFromGitHub because it uses a name like so: "${repo}-${rev}-src"

Fixes #5954

pkgs/build-support/fetchzip/default.nix

@@ -28,7 +28,7 @@ lib.overrideDerivation (fetchurl ({
       mkdir "$unpackDir"
       cd "$unpackDir"
 
-      renamed="$TMPDIR/$name"
+      renamed="$TMPDIR/${baseNameOf url}"
       mv "$downloadedFile" "$renamed"
       unpackFile "$renamed"