ref(discover): Fix y-axis copy for count_unique (#25983)

We could alternatively switch this to english language but if we are going to make the copy column-esque it should at least be a valid discover column.

static/app/utils/discover/types.tsx

@@ -37,5 +37,5 @@ export const DISPLAY_MODE_FALLBACK_OPTIONS = {
 // default list of yAxis options
 export const CHART_AXIS_OPTIONS = [
   {label: 'count()', value: 'count()'},
-  {label: 'count_unique(users)', value: 'count_unique(user)'},
+  {label: 'count_unique(user)', value: 'count_unique(user)'},
 ];