Typeshed cherry-pick: Fix @patch when new is missing (#10459)

[svalentin]

For release-1.5

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

streamlit (https://github.com/streamlit/streamlit)
- lib/tests/streamlit/config_test.py:619:9: error: "_patch[Union[MagicMock, AsyncMock]]" has no attribute "return_value"  [attr-defined]
+ lib/tests/streamlit/config_test.py:619:9: error: "_patch_default_new" has no attribute "return_value"  [attr-defined]
- lib/tests/streamlit/config_test.py:621:9: error: "_patch[Union[MagicMock, AsyncMock]]" has no attribute "side_effect"  [attr-defined]
+ lib/tests/streamlit/config_test.py:621:9: error: "_patch_default_new" has no attribute "side_effect"  [attr-defined]
- lib/tests/streamlit/config_test.py:645:9: error: "_patch[Union[MagicMock, AsyncMock]]" has no attribute "return_value"  [attr-defined]
+ lib/tests/streamlit/config_test.py:645:9: error: "_patch_default_new" has no attribute "return_value"  [attr-defined]
- lib/tests/streamlit/config_test.py:647:9: error: "_patch[Union[MagicMock, AsyncMock]]" has no attribute "side_effect"  [attr-defined]
+ lib/tests/streamlit/config_test.py:647:9: error: "_patch_default_new" has no attribute "side_effect"  [attr-defined]
- lib/tests/streamlit/config_test.py:683:9: error: "_patch[Union[MagicMock, AsyncMock]]" has no attribute "return_value"  [attr-defined]
+ lib/tests/streamlit/config_test.py:683:9: error: "_patch_default_new" has no attribute "return_value"  [attr-defined]
- lib/tests/streamlit/config_test.py:685:9: error: "_patch[Union[MagicMock, AsyncMock]]" has no attribute "side_effect"  [attr-defined]
+ lib/tests/streamlit/config_test.py:685:9: error: "_patch_default_new" has no attribute "side_effect"  [attr-defined]
- lib/tests/streamlit/config_test.py:731:9: error: "_patch[Union[MagicMock, AsyncMock]]" has no attribute "return_value"  [attr-defined]
+ lib/tests/streamlit/config_test.py:731:9: error: "_patch_default_new" has no attribute "return_value"  [attr-defined]
- lib/tests/streamlit/config_test.py:733:9: error: "_patch[Union[MagicMock, AsyncMock]]" has no attribute "side_effect"  [attr-defined]
+ lib/tests/streamlit/config_test.py:733:9: error: "_patch_default_new" has no attribute "side_effect"  [attr-defined]
- lib/tests/streamlit/config_test.py:757:9: error: "_patch[Union[MagicMock, AsyncMock]]" has no attribute "return_value"  [attr-defined]
+ lib/tests/streamlit/config_test.py:757:9: error: "_patch_default_new" has no attribute "return_value"  [attr-defined]
- lib/tests/streamlit/config_test.py:759:9: error: "_patch[Union[MagicMock, AsyncMock]]" has no attribute "side_effect"  [attr-defined]
+ lib/tests/streamlit/config_test.py:759:9: error: "_patch_default_new" has no attribute "side_effect"  [attr-defined]
- lib/tests/streamlit/config_test.py:793:9: error: "_patch[Union[MagicMock, AsyncMock]]" has no attribute "return_value"  [attr-defined]
+ lib/tests/streamlit/config_test.py:793:9: error: "_patch_default_new" has no attribute "return_value"  [attr-defined]
- lib/tests/streamlit/config_test.py:795:9: error: "_patch[Union[MagicMock, AsyncMock]]" has no attribute "side_effect"  [attr-defined]
+ lib/tests/streamlit/config_test.py:795:9: error: "_patch_default_new" has no attribute "side_effect"  [attr-defined]