[Checkbox] Update unselected outline color to ?attr/colorOnSurfaceVariant to match tokens.

PiperOrigin-RevId: 484295821

Author: leticiarossi

lib/java/com/google/android/material/checkbox/res/color/m3_checkbox_button_tint.xml

@@ -31,5 +31,5 @@
   <item android:color="@macro/m3_comp_checkbox_selected_container_color" android:state_checked="true"/>
 
   <!-- Unchecked -->
-  <item android:color="?attr/colorOnSurface" android:state_checked="false"/>
+  <item android:color="@macro/m3_comp_checkbox_unselected_outline_color" android:state_checked="false"/>
 </selector>

lib/java/com/google/android/material/checkbox/res/values/tokens.xml

@@ -20,6 +20,7 @@
 <resources>
   <!-- Generated from token set (md.comp.checkbox) in default context. -->
   <!-- Enabled - Container -->
+  <macro name="m3_comp_checkbox_unselected_outline_color">?attr/colorOnSurfaceVariant</macro>
   <macro name="m3_comp_checkbox_selected_container_color">?attr/colorPrimary</macro>
   <macro name="m3_comp_checkbox_selected_error_container_color">?attr/colorError</macro>
   <!-- Enabled - Icon -->