Analysis: Resolve non exhaustive when statements when warning

Warning Message: "Non exhaustive 'when' statements on enum will be
prohibited in 1.7, add 'ADD_MEDIA_COLLAPSE', 'ADD_MEDIA_EXPAND',
'HIGHLIGHT', 'UNORDERED_LIST', 'ORDERED_LIST', 'TASK_LIST', 'INDENT',
... branches or 'else' branch instead"

aztec/src/main/kotlin/org/wordpress/aztec/toolbar/AztecToolbar.kt

@@ -791,6 +791,7 @@ class AztecToolbar : FrameLayout, IAztecToolbar, OnMenuItemClickListener {
                 when (toolbarAction) {
                     ToolbarAction.HEADING -> setHeadingMenu(it)
                     ToolbarAction.LIST -> setListMenu(it)
+                    else -> Unit // Do nothing
                 }
                 if (!hasCustomLayout) {
                     it.setBackgroundDrawableRes(toolbarAction.buttonDrawableRes)