MM-25006: Fix occurences of unclosed http bodies (#14521)

* MM-25006: Fix occurences of unclosed http bodies

And while here, we also use ioutil.Discard to read the remaining
body instead of reading with ioutil.ReadAll which allocates a separate
byte buffer.

* Fix mistake

* Address review comments

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

app/security_update_check.go

@@ -106,7 +106,7 @@ func (s *Server) DoSecurityUpdateCheck() {
 					}
 
 					body, err := ioutil.ReadAll(resBody.Body)
-					res.Body.Close()
+					resBody.Body.Close()
 					if err != nil || resBody.StatusCode != 200 {
 						mlog.Error("Failed to read security bulletin details")
 						return