Switch xonsh source from PyPI to GitHub tag, add Woodpecker CI

Use fetchFromGitHub with tag = version so the version string and
source are inherently linked via rec. Adds .woodpecker.yaml to
build all flake packages on tag push.

.woodpecker.yaml

@@ -0,0 +1,15 @@
+when:
+  - event: tag
+    ref: "refs/tags/v*"
+
+steps:
+  - name: build
+    image: git.oleks.space/oleks/nix-ci:latest
+    commands:
+      - echo "extra-experimental-features = nix-command flakes" >> /etc/nix/nix.conf
+      - nix build .#xonsh --no-link --print-out-paths
+      - nix build .#hello-world --no-link --print-out-paths
+    backend_options:
+      kubernetes:
+        nodeSelector:
+          kubernetes.io/hostname: howard2404

flake.nix

@@ -31,8 +31,7 @@
         hello-world = pkgs.callPackage ./packages/hello-world.nix { };
         xonsh = pkgs.callPackage ./packages/xonsh.nix {
           xonsh-unwrapped = import ./packages/xonsh-unwrapped.nix {
-            inherit (pkgs) lib;
-            inherit (pkgs) python3Packages;
+            inherit (pkgs) lib python3Packages fetchFromGitHub;
           };
         };
       };

packages/xonsh-unwrapped.nix

@@ -1,12 +1,14 @@
-{ lib, python3Packages }:
+{ lib, python3Packages, fetchFromGitHub }:
 
 python3Packages.buildPythonPackage rec {
   pname = "xonsh";
   version = "0.22.7";
 
-  src = python3Packages.fetchPypi {
-    inherit pname version;
-    sha256 = "sha256-gPApjBEctw1eLWN5gtz0ArJXPOcSqwyBNJBHdFMdRwk=";
+  src = fetchFromGitHub {
+    owner = "xonsh";
+    repo = "xonsh";
+    tag = version;
+    hash = "sha256-2Gvd7jOKhouorE8wH4FaWlaw8y1h4uf/Z+sYWO96Vps=";
   };
 
   # xonsh uses pyproject.toml setuptools