Fix typo in rollup_index definition (#40520)

Author: jrodewig

docs/reference/rollup/apis/rollup-job-config.asciidoc

@@ -69,7 +69,7 @@ In the above example, there are several pieces of logistical configuration for t
 `rollup_index` (required)::
   (string) The index that you wish to store rollup results into.   All the rollup data that is generated by the job will be
   stored in this index.  When searching the rollup data, this index will be used in the <<rollup-search,Rollup Search>> endpoint's URL.
-  The rollup index be shared with other rollup jobs.  The data is stored so that it doesn't interfere with unrelated jobs.
+  The rollup index can be shared with other rollup jobs.  The data is stored so that it doesn't interfere with unrelated jobs.
 
 `cron` (required)::
   (string) A cron string which defines when the rollup job should be executed.  The cron string defines an interval of when to run