v8.0 module release (#22975)

https://mattermost.atlassian.net/browse/MM-52079

```release-note
We upgrade the module version to 8.0. The new module path is github.com/mattermost-server/server/v8.
```


Co-authored-by: Doug Lauder <wiggin77@warpmail.net>

server/boards/utils/callbackqueue_test.go

@@ -11,7 +11,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 
-	"github.com/mattermost/mattermost-server/v6/server/platform/shared/mlog"
+	"github.com/mattermost/mattermost-server/server/v8/platform/shared/mlog"
 )
 
 func Test_newChangeNotifier(t *testing.T) {