Slightly increase maximum width of legend items in text only face

Otherwise we switch to two columns too early and we end up with cramped
text in plasma-systemmonitor's overview page.

faces/facepackages/textonly/contents/ui/GroupedText.qml

@@ -111,7 +111,7 @@ ColumnLayout {
 
                     Charts.LegendLayout.minimumWidth: minimumWidth
                     Charts.LegendLayout.preferredWidth: preferredWidth
-                    Charts.LegendLayout.maximumWidth: Math.max(preferredWidth, Kirigami.Units.gridUnit * 15)
+                    Charts.LegendLayout.maximumWidth: Math.max(preferredWidth, Kirigami.Units.gridUnit * 17)
                 }
             }