Fix #8883: autodoc: AttributeError on assigning __annotations__

CHANGES

@@ -16,6 +16,8 @@ Features added
 Bugs fixed
 ----------
 
+* #8883: autodoc: AttributeError is raised on assigning __annotations__ on
+  read-only class
 * #8884: html: minified js stemmers not included in the distributed package
 * #8880: viewcode: ExtensionError is raised on incremental build after
   unparsable python module found

sphinx/ext/autodoc/__init__.py

@@ -1394,7 +1394,7 @@ class FunctionDocumenter(DocstringSignatureMixin, ModuleLevelDocumenter):  # typ
             params[0] = params[0].replace(annotation=typ)
             try:
                 func.__signature__ = sig.replace(parameters=params)  # type: ignore
-            except TypeError:
+            except (AttributeError, TypeError):
                 # failed to update signature (ex. built-in or extension types)
                 return
 
@@ -2177,7 +2177,7 @@ class MethodDocumenter(DocstringSignatureMixin, ClassLevelDocumenter):  # type:
             params[1] = params[1].replace(annotation=typ)
             try:
                 func.__signature__ = sig.replace(parameters=params)  # type: ignore
-            except TypeError:
+            except (AttributeError, TypeError):
                 # failed to update signature (ex. built-in or extension types)
                 return
 
@@ -2443,7 +2443,7 @@ class AttributeDocumenter(GenericAliasMixin, NewTypeMixin, SlotsMixin,  # type:
                             annotations[attrname] = annotation
                 except (AttributeError, PycodeError):
                     pass
-        except TypeError:
+        except (AttributeError, TypeError):
             # Failed to set __annotations__ (built-in, extensions, etc.)
             pass