python3Packages.pypng: ref -> tag, nativeBuildInputs -> build-system

`hash` did not change

Changed files
+2 -2
pkgs
development
python-modules
pypng
+2 -2
pkgs/development/python-modules/pypng/default.nix
···
src = fetchFromGitLab {
owner = "drj11";
repo = "pypng";
-
rev = "refs/tags/${pname}-${version}";
+
tag = "pypng-${version}";
hash = "sha256-tTnsGCAmHexDWm/T5xpHpcBaQcBEqMfTFaoOAeC+pDs=";
};
-
nativeBuildInputs = [ setuptools ];
+
build-system = [ setuptools ];
patches = [
# pngsuite is imported by code/test_png.py but is not defined in