[skip ci] Add comment for addReleasedPartition (#9244)

Signed-off-by: bigsheeper <yihao.dai@zilliz.com>

internal/querynode/collection.go

@@ -148,6 +148,7 @@ func (c *Collection) getReleaseTime() Timestamp {
 	return c.releaseTime
 }
 
+// addReleasedPartition records the partition to indicate that this partition has been released
 func (c *Collection) addReleasedPartition(partitionID UniqueID) {
 	c.releaseMu.Lock()
 	defer c.releaseMu.Unlock()