Bump golangci to use 1.18 (#20010)

https://mattermost.atlassian.net/browse/MM-42148

```release-note
NONE
```

utils/markdown.go

@@ -141,7 +141,7 @@ func (r *notificationRenderer) renderText(w util.BufWriter, source []byte, node
 
 func (r *notificationRenderer) renderTextBlock(w util.BufWriter, _ []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
 	if !entering {
-		if _, ok := node.NextSibling().(ast.Node); ok && node.FirstChild() != nil {
+		if node.NextSibling() != nil && node.FirstChild() != nil {
 			_ = w.WriteByte(' ')
 		}
 	}