docs: use double quotes for cross-platform compatibility in example code

doc/en/example/markers.rst

@@ -80,7 +80,7 @@ keyword arguments, e.g. to run only tests marked with ``device`` and the specifi
 
 .. code-block:: pytest
 
-    $ pytest -v -m 'device(serial="123")'
+    $ pytest -v -m "device(serial='123')"
     =========================== test session starts ============================
     platform linux -- Python 3.x.y, pytest-8.x.y, pluggy-1.x.y -- $PYTHON_PREFIX/bin/python
     cachedir: .pytest_cache

doc/en/how-to/usage.rst

@@ -88,7 +88,7 @@ with the ``phase`` keyword argument set to ``1``:
 
 .. code-block:: bash
 
-    pytest -m slow(phase=1)
+    pytest -m "slow(phase=1)"
 
 For more information see :ref:`marks <mark>`.