python3Packages.solidpython2: skip example 18 with missing reference fixture (#523370)

pkgs/development/python-modules/solidpython2/difftool_tests.patch

@@ -2,7 +2,16 @@ diff --git a/tests/examples_test.py b/tests/examples_test.py
 index 77204fd..9784389 100644
 --- a/tests/examples_test.py
 +++ b/tests/examples_test.py
-@@ -48,14 +48,19 @@ class ExamplesTest(unittest.TestCase):
+@@ -41,6 +41,8 @@ class ExamplesTest(unittest.TestCase):
+                 continue
+             if f.stem.endswith(".x"):
+                 continue
++            if f.stem.startswith("18-"):
++                continue
+
+             test_scad_file = root / "tests" / "examples_scad" \
+                              / f.with_suffix('.scad').name
+@@ -48,14 +50,19 @@ class ExamplesTest(unittest.TestCase):
              subprocess.check_call(["python3", f.as_posix()])
              # copy generated scad file to examples_scad/
              copyWithRelativeIncludes(f.with_suffix(".scad"), test_scad_file)