Update title for err handling in Go

Apply suggestion in https://gitlab.com/gitlab-org/gitlab/-/merge_requests/29860#note_342933415

doc/development/go_guide/index.md

@@ -249,7 +249,7 @@ Programs handling a lot of IO or complex operations should always include
 [benchmarks](https://golang.org/pkg/testing/#hdr-Benchmarks), to ensure
 performance consistency over time.
 
-## Using errors
+## Error handling
 
 ### Adding context