Fix unspecified-encoding warnings in tests (#119405)

tests/test_block_async_io.py

@@ -208,7 +208,7 @@ async def test_protect_loop_open(caplog: pytest.LogCaptureFixture) -> None:
     """Test open of a file in /proc is not reported."""
     block_async_io.enable()
     with contextlib.suppress(FileNotFoundError):
-        open("/proc/does_not_exist").close()
+        open("/proc/does_not_exist", encoding="utf8").close()
     assert "Detected blocking call to open with args" not in caplog.text
 
 
@@ -216,7 +216,7 @@ async def test_protect_open(caplog: pytest.LogCaptureFixture) -> None:
     """Test opening a file in the event loop logs."""
     block_async_io.enable()
     with contextlib.suppress(FileNotFoundError):
-        open("/config/data_not_exist").close()
+        open("/config/data_not_exist", encoding="utf8").close()
 
     assert "Detected blocking call to open with args" in caplog.text
 
@@ -233,7 +233,7 @@ async def test_protect_open_path(path: Any, caplog: pytest.LogCaptureFixture) ->
     """Test opening a file by path in the event loop logs."""
     block_async_io.enable()
     with contextlib.suppress(FileNotFoundError):
-        open(path).close()
+        open(path, encoding="utf8").close()
 
     assert "Detected blocking call to open with args" in caplog.text