fix: test nested blocks with what CI installs

The rendering test imported pymdownx, which the CI test job does not install. An admonition nests its body by the same four spaces, so the test uses it and needs only markdown.

tests/test_site_exports.py

@@ -843,16 +843,15 @@ class NestedProfileBlocksRenderAsLists(unittest.TestCase):
     def _html(self, value: object) -> str:
         try:
             import markdown
-            import pymdownx.details  # noqa: F401
         except ImportError:
-            self.skipTest("markdown and pymdown-extensions are not installed")
+            self.skipTest("markdown is not installed")
         from siterender import _render_yaml_value
 
-        lines = ['???+ abstract "Analysis"', ""]
+        # The page opens the block with ???+ (pymdownx.details). An admonition
+        # nests its body by the same four spaces, and needs nothing CI lacks.
+        lines = ['!!! abstract "Analysis"', ""]
         _render_yaml_value(lines, value, 4)
-        return markdown.markdown(
-            "\n".join(lines), extensions=["admonition", "pymdownx.details"]
-        )
+        return markdown.markdown("\n".join(lines), extensions=["admonition"])
 
     def test_a_nested_mapping_is_a_nested_list(self):
         html = self._html({"megacd_bios": {"external_required": False, "source_ref": "a.c:1"},