autodoc: Reset `sys.modules` on partial import failure (#11645)

If importing with ``TYPE_CHECKING is True`` fails, reset the state of ``sys.modules``
so that the attempt with ``TYPE_CHECKING is False`` may succeed.

Co-authored-by: Adam Turner <9087854+aa-turner@users.noreply.github.com>

tests/roots/test-ext-autodoc/circular_import/__init__.py

@@ -0,0 +1 @@
+from circular_import.c import SomeClass

tests/roots/test-ext-autodoc/circular_import/a.py

@@ -0,0 +1 @@
+X = 42

tests/roots/test-ext-autodoc/circular_import/b.py

@@ -0,0 +1,4 @@
+import typing
+
+if typing.TYPE_CHECKING:
+    from circular_import import SomeClass

tests/roots/test-ext-autodoc/circular_import/c.py

@@ -0,0 +1,6 @@
+import circular_import.a
+import circular_import.b
+
+
+class SomeClass:
+    X = circular_import.a.X

tests/test_ext_autodoc.py

@@ -2024,6 +2024,19 @@ def test_autodoc_TYPE_CHECKING(app):
     ]
 
 
+@pytest.mark.sphinx('html', testroot='ext-autodoc')
+def test_autodoc_TYPE_CHECKING_circular_import(app):
+    options = {"members": None,
+               "undoc-members": None}
+    actual = do_autodoc(app, 'module', 'circular_import', options)
+    assert list(actual) == [
+        '',
+        '.. py:module:: circular_import',
+        '',
+    ]
+    assert sys.modules["circular_import"].a is sys.modules["circular_import.a"]
+
+
 @pytest.mark.sphinx('html', testroot='ext-autodoc')
 def test_singledispatch(app):
     options = {"members": None}