Propagate Sync error when running SafeFileRotate (elastic#9069)

Previously, it was possible SafeFileRotate encountered an error without propagating it, because the return value of os.Sync was not utilized.
From now on the errors from Sync are propagated.
(cherry picked from commit 93eb92a)

CHANGELOG.asciidoc

@@ -33,6 +33,12 @@ https://github.com/elastic/beats/compare/v6.5.0...6.5[Check the HEAD diff]
 
 *Affecting all Beats*
 
+- Fixed `-d` CLI flag by trimming spaces from selectors. {pull}7864[7864]
+- Fixed Support `add_docker_metadata` in Windows by identifying systems' path separator. {issue}7797[7797]
+- Do not panic when no tokenizer string is configured for a dissect processor. {issue}8895[8895]
+- Start autodiscover consumers before producers. {pull}7926[7926]
+- Propagate Sync error when running SafeFileRotate. {pull}9069[9069]
+
 *Auditbeat*
 
 *Filebeat*

libbeat/common/file/helper_other.go

@@ -40,7 +40,6 @@ func SafeFileRotate(path, tempfile string) error {
 		return nil // ignore error
 	}
 	defer f.Close()
-	f.Sync()
 
-	return nil
+	return f.Sync()
 }