Use session dbus mocks for all tests (#4198)

* Use session dbus mocks for all tests

* func instead of fn for pylint

tests/dbus_service_mocks/agent_boards.py

@@ -0,0 +1,31 @@
+"""Mock of OS Agent Boards dbus service."""
+
+from dbus_fast.service import PropertyAccess, dbus_property
+
+from .base import DBusServiceMock
+
+BUS_NAME = "io.hass.os"
+
+
+def setup(object_path: str | None = None) -> DBusServiceMock:
+    """Create dbus mock object."""
+    return Boards()
+
+
+# pylint: disable=invalid-name
+
+
+class Boards(DBusServiceMock):
+    """Boards mock.
+
+    gdbus introspect --system --dest io.hass.os --object-path /io/hass/os/Boards
+    """
+
+    object_path = "/io/hass/os/Boards"
+    interface = "io.hass.os.Boards"
+    board = "Yellow"
+
+    @dbus_property(access=PropertyAccess.READ)
+    def Board(self) -> "s":
+        """Get Board."""
+        return self.board