Reword the string "pref_failed_to_sync" (#4134)

This changes one word in the string `pref_failed_to_sync` in the file
`values/strings.xml`.

See my reasoning here #4133 

"Failed to sync settings" changes to "Failed to sync preferences".

app/src/main/res/values/strings.xml

@@ -334,7 +334,7 @@
     <string name="pref_default_post_language">Default posting language</string>
     <string name="pref_default_media_sensitivity">Always mark media as sensitive</string>
     <string name="pref_publishing">Publishing (synced with server)</string>
-    <string name="pref_failed_to_sync">Failed to sync settings</string>
+    <string name="pref_failed_to_sync">Failed to sync preferences</string>
 
     <string name="pref_main_nav_position">Main navigation position</string>
     <string name="pref_main_nav_position_option_top">Top</string>