libpeas2: Fix Python loader

Signed-off-by: Federico Damián Schonborn <fdschonborn@gmail.com>

pkgs/development/libraries/libpeas/2.x.nix

@@ -1,6 +1,7 @@
 { stdenv
 , lib
 , fetchurl
+, substituteAll
 , pkg-config
 , gi-docgen
 , gobject-introspection
@@ -25,6 +26,16 @@ stdenv.mkDerivation rec {
     hash = "sha256-ndwdUfOGY9pN9SFjBRt7LOo6JCz67p9afhQPB4TIqnc=";
   };
 
+  patches = [
+    # Make PyGObject’s gi library available.
+    (substituteAll {
+      src = ./fix-paths.patch;
+      pythonPaths = lib.concatMapStringsSep ", " (pkg: "'${pkg}/${python3.sitePackages}'") [
+        python3.pkgs.pygobject3
+      ];
+    })
+  ];
+
   depsBuildBuild = [
     pkg-config
   ];