MM-60387: Bump Go version to 1.22 (#28118)

https://mattermost.atlassian.net/browse/MM-60387
```release-note
updated Go version to 1.22
```
---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/go.mod

@@ -1,8 +1,8 @@
 module github.com/mattermost/mattermost/server/v8
 
-go 1.21.0
+go 1.22.0
 
-toolchain go1.21.8
+toolchain go1.22.6
 
 require (
 	code.sajari.com/docconv/v2 v2.0.0-pre.4