Mock session to avoid Windows issues on CI.

Instantiating a real session on Windows CI leads to exception:

```
prompt_toolkit.output.win32.NoConsoleScreenBufferError: No Windows console found. Are you running cmd.exe?
```

with the following traceback:

```
IPython\terminal\tests\test_shortcuts.py:214:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
C:\hostedtoolcache\windows\PyPy\3.8.15\x86\lib\site-packages\prompt_toolkit\shortcuts\prompt.py:476: in __init__
    self.app = self._create_application(editing_mode, erase_when_done)
C:\hostedtoolcache\windows\PyPy\3.8.15\x86\lib\site-packages\prompt_toolkit\shortcuts\prompt.py:765: in _create_application
    output=self._output,
C:\hostedtoolcache\windows\PyPy\3.8.15\x86\lib\site-packages\prompt_toolkit\application\application.py:282: in __init__
    self.output = output or session.output
C:\hostedtoolcache\windows\PyPy\3.8.15\x86\lib\site-packages\prompt_toolkit\application\current.py:71: in output
    self._output = create_output()
C:\hostedtoolcache\windows\PyPy\3.8.15\x86\lib\site-packages\prompt_toolkit\output\defaults.py:85: in create_output
    return Win32Output(stdout, default_color_depth=color_depth_from_env)
C:\hostedtoolcache\windows\PyPy\3.8.15\x86\lib\site-packages\prompt_toolkit\output\win32.py:114: in __init__
    info = self.get_win32_screen_buffer_info()
```

IPython/terminal/tests/test_shortcuts.py

@@ -11,7 +11,6 b' from IPython.terminal.shortcuts.auto_suggest import ('
 )
 
 from prompt_toolkit.history import InMemoryHistory
-from prompt_toolkit.shortcuts import PromptSession
 from prompt_toolkit.buffer import Buffer
 
 from unittest.mock import patch, Mock
@@ -207,18 +206,24 b' async def test_navigable_provider():'
     assert get_suggestion().text == "_a"
 
 
+def create_session_mock():
+    session = Mock()
+    session.default_buffer = Buffer()
+    return session
+
+
 def test_navigable_provider_connection():
     provider = NavigableAutoSuggestFromHistory()
     provider.skip_lines = 1
 
-    session_1 = PromptSession()
+    session_1 = create_session_mock()
     provider.connect(session_1)
 
     assert provider.skip_lines == 1
     session_1.default_buffer.on_text_insert.fire()
     assert provider.skip_lines == 0
 
-    session_2 = PromptSession()
+    session_2 = create_session_mock()
     provider.connect(session_2)
     provider.skip_lines = 2