docs: enable nitpicky mode

Catch broken references.

docs/conf.py

@@ -61,6 +61,19 @@
 
 autodoc_member_order = "bysource"
 
+nitpicky = True
+nitpick_ignore = {
+    # Don't want to expose this yet (see #428).
+    ("py:class", "pluggy._tracing.TagTracerSub"),
+    # Compat hack, don't want to expose it.
+    ("py:class", "pluggy._manager.DistFacade"),
+    # `types.ModuleType` turns into `module` but then fails to resolve...
+    ("py:class", "module"),
+    # Just a TypeVar.
+    ("py:obj", "pluggy._result.ResultType"),
+    ("py:class", "pluggy._result.ResultType"),
+}
+
 # -- Options for Texinfo output -------------------------------------------
 
 # Grouping the document tree into Texinfo files. List of tuples

src/pluggy/_manager.py

@@ -174,7 +174,7 @@ def parse_hookimpl_opts(self, plugin: _Plugin, name: str) -> HookimplOpts | None
 
         This method can be overridden by ``PluginManager`` subclasses to
         customize how hook implementation are picked up. By default, returns the
-        options for items decorated with :class:`HookImplMarker`.
+        options for items decorated with :class:`HookimplMarker`.
         """
         method: object = getattr(plugin, name)
         if not inspect.isroutine(method):