Bump Go version to 1.23.6 (#30242)

* Bump Go version to 1.23.6

* Update CodeQL Github action as well

* Use server's Go version for CodeQL action

Co-authored-by: Antonis Stamatiou <stamatiou.antonis@gmail.com>

* Empty commit to trigger CI

* Bump golangci-lint to a version supporting Go 1.23

* Fix golangci-lint warnings

Several rules from gosimple, revive and staticcheck linters were
failing:
- Redefinition of built-in identifiers (max, min, new, recover...)
- Use of printf-like functions with simple strings
- Check for nil slices, when len already takes it into account

---------

Co-authored-by: Antonis Stamatiou <stamatiou.antonis@gmail.com>
Co-authored-by: Mattermost Build <build@mattermost.com>

server/platform/shared/mail/inbucket.go

@@ -103,7 +103,7 @@ func GetMessageFromMailbox(email, id string) (JSONMessageInbucket, error) {
 	}
 
 	// download attachments
-	if record.Attachments != nil && len(record.Attachments) > 0 {
+	if len(record.Attachments) > 0 {
 		for i := range record.Attachments {
 			var bytes []byte
 			bytes, err = downloadAttachment(record.Attachments[i].DownloadLink)