[SPARK-52188][FOLLOWUP] Update comment in getRunId

### What changes were proposed in this pull request?

#50924 removed the logic of generating a random id in `StateStoreProvider.getRunId` didn't update the comment. Following discussion here, update the comment #51304 (comment)

### Why are the changes needed?

Code readability

### Does this PR introduce _any_ user-facing change?

No

### How was this patch tested?

No need

### Was this patch authored or co-authored using generative AI tooling?

No

Closes #51307 from WweiL/SPARK-52188-followup.

Authored-by: Wei Liu <[email protected]>
Signed-off-by: yangjie01 <[email protected]>

Author: WweiL

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/StateStore.scala

@@ -664,7 +664,7 @@ object StateStoreProvider extends Logging {
   }
 
   /**
-   * Get the runId from the provided hadoopConf. If it is not found, generate a random UUID.
+   * Get the runId from the provided hadoopConf. If it is not found, an error will be thrown.
    *
    * @param hadoopConf Hadoop configuration used by the StateStore to save state data
    */