MM-53032: Fix module path after repo rename (#23689)

It was a good decision in hindsight to keep the public module as 0.x
because this would have been a breaking change again.

https://mattermost.atlassian.net/browse/MM-53032
```release-note
Changed the Go module path from github.com/mattermost/mattermost-server/server/v8 to github.com/mattermost/mattermost/server/v8.

For the public facing module, it's path is also changed from github.com/mattermost/mattermost-server/server/public to github.com/mattermost/mattermost/server/public
```

server/channels/web/web_test.go

@@ -17,15 +17,15 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
-	"github.com/mattermost/mattermost-server/server/public/model"
-	"github.com/mattermost/mattermost-server/server/public/plugin"
-	"github.com/mattermost/mattermost-server/server/public/plugin/utils"
-	"github.com/mattermost/mattermost-server/server/public/shared/mlog"
-	"github.com/mattermost/mattermost-server/server/v8/channels/app"
-	"github.com/mattermost/mattermost-server/server/v8/channels/app/request"
-	"github.com/mattermost/mattermost-server/server/v8/channels/store/localcachelayer"
-	"github.com/mattermost/mattermost-server/server/v8/channels/store/storetest/mocks"
-	"github.com/mattermost/mattermost-server/server/v8/config"
+	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/public/plugin"
+	"github.com/mattermost/mattermost/server/public/plugin/utils"
+	"github.com/mattermost/mattermost/server/public/shared/mlog"
+	"github.com/mattermost/mattermost/server/v8/channels/app"
+	"github.com/mattermost/mattermost/server/v8/channels/app/request"
+	"github.com/mattermost/mattermost/server/v8/channels/store/localcachelayer"
+	"github.com/mattermost/mattermost/server/v8/channels/store/storetest/mocks"
+	"github.com/mattermost/mattermost/server/v8/config"
 )
 
 var apiClient *model.Client4
@@ -205,7 +205,7 @@ func TestStaticFilesRequest(t *testing.T) {
 	package main
 
 	import (
-		"github.com/mattermost/mattermost-server/server/public/plugin"
+		"github.com/mattermost/mattermost/server/public/plugin"
 	)
 
 	type MyPlugin struct {
@@ -292,7 +292,7 @@ func TestPublicFilesRequest(t *testing.T) {
 	package main
 
 	import (
-		"github.com/mattermost/mattermost-server/server/public/plugin"
+		"github.com/mattermost/mattermost/server/public/plugin"
 	)
 
 	type MyPlugin struct {