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/app/integration_action_test.go

@@ -16,7 +16,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
-	"github.com/mattermost/mattermost-server/server/public/model"
+	"github.com/mattermost/mattermost/server/public/model"
 )
 
 // Test for MM-13598 where an invalid integration URL was causing a crash
@@ -548,8 +548,8 @@ func TestSubmitInteractiveDialog(t *testing.T) {
 			"net/http"
 			"encoding/json"
 
-			"github.com/mattermost/mattermost-server/server/public/plugin"
-			"github.com/mattermost/mattermost-server/server/public/model"
+			"github.com/mattermost/mattermost/server/public/plugin"
+			"github.com/mattermost/mattermost/server/public/model"
 		)
 
 		type MyPlugin struct {
@@ -840,8 +840,8 @@ func TestPostActionRelativePluginURL(t *testing.T) {
 			"net/http"
 			"encoding/json" 
 
-			"github.com/mattermost/mattermost-server/server/public/plugin"
-			"github.com/mattermost/mattermost-server/server/public/model"
+			"github.com/mattermost/mattermost/server/public/plugin"
+			"github.com/mattermost/mattermost/server/public/model"
 		)
 
 		type MyPlugin struct {
@@ -1042,7 +1042,7 @@ func TestDoPluginRequest(t *testing.T) {
 			"reflect"
 			"sort"
 
-			"github.com/mattermost/mattermost-server/server/public/plugin"
+			"github.com/mattermost/mattermost/server/public/plugin"
 		)
 
 		type MyPlugin struct {