weechatScripts.weechat-matrix: fix matrix_sso_helper path

server.py tries to launch a matrix_sso_helper binary when connecting to
a homeserver that uses some SSO mechanism instead of plain login and
password, but doesn't have $out/bin in $PATH.

Using substituteInPlace to patch server.py so that the helper process is
started by using its actual filesystem location instead of relying on
$PATH.

Fixes: https://github.com/NixOS/nixpkgs/issues/124186

pkgs/applications/networking/irc/weechat/scripts/weechat-matrix/default.nix

@@ -73,6 +73,7 @@ in buildPythonPackage {
   postFixup = ''
     addToSearchPath program_PYTHONPATH $out/${python.sitePackages}
     patchPythonScript $out/share/matrix.py
+    substituteInPlace $out/${python.sitePackages}/matrix/server.py --replace \"matrix_sso_helper\" \"$out/bin/matrix_sso_helper\"
   '';
 
   meta = with lib; {