[Wi-Fi] Fix hint text color contrast problem in 'Add networks'

To raise hint text color, set android:attr/textColorSecondary
to android:textColorHint.

Bug: 146908018
Test: accessibility scanner
Change-Id: Id2525c1a0fc0b3f95298d493e2dc69b91aa13d77

res/layout/wifi_dialog.xml

@@ -470,7 +470,7 @@
                     <EditText android:id="@+id/proxy_pac"
                             android:layout_width="match_parent"
                             android:layout_height="wrap_content"
-                            style="@style/wifi_item_content"
+                            style="@style/wifi_item_edit_content"
                             android:hint="@string/proxy_url_hint"
                             android:inputType="textNoSuggestions"
                             android:singleLine="true"/>