ci: pin playwright similar to solara for compatibility

As mentioned in widgetti/solara#913
pytest-ipywidgets is not compatible with newer versions of
pytest-playwright.
We did not notice this in solara, because we pinned playwright, which
seems to limit the versions of pytest-playwright to a compatible one.
If we apply the same pinning as solara, we should be able to avoid
this issue.

setup.cfg

@@ -35,7 +35,7 @@ test =
     pytest-cov
     nbconvert>=6.4.5
 visualtest =
-    playwright
+    playwright==1.41.2
     pytest-playwright
     pytest-mpl
     solara[pytest]