python3Packages.deal: skip missing docstring-parser tests

docstring-parser 0.18 no longer ships its tests in built wheels, so deal's
test suite fails during collection when it tries to read
docstring_parser/tests. Skip generating the cross-check cases when the
directory is absent.

Assisted-by: OpenCode 2 (DeepSeek V4.1 Flash Free)

pkgs/development/python-modules/deal/default.nix

@@ -30,6 +30,11 @@ buildPythonPackage rec {
     hash = "sha256-nLZ06Xfa9Q+Saf8qPXG1Xo6y6oO6kifhfK/gryZ6q90=";
   };
 
+  patches = [
+    # docstring-parser 0.18 no longer ships its tests, which this test reads.
+    ./skip-missing-docstring-parser-tests.patch
+  ];
+
   build-system = [ flit-core ];
 
   dependencies = [

pkgs/development/python-modules/deal/skip-missing-docstring-parser-tests.patch

@@ -0,0 +1,16 @@
+docstring_parser 0.18 excludes its tests from built wheels, so
+`docstring_parser.__path__[0] / 'tests'` does not exist and test
+collection fails with FileNotFoundError. Skip generating the cross-check
+test cases when the directory is unavailable.
+
+--- a/tests/test_linter/test_extractors/test_exceptions.py
++++ b/tests/test_linter/test_extractors/test_exceptions.py
+@@ -293,6 +293,8 @@ def get_docstring_parser_tests():
+     tests_found = 0
+     if astroid is None:
+         return
++    if not root.is_dir():
++        return
+     for path in root.iterdir():
+         if path.suffix != '.py':
+             continue