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/public/plugin/checker/check_api_test.go

@@ -17,24 +17,24 @@ func TestCheckAPIVersionComments(t *testing.T) {
 	}{
 		{
 			name:    "valid comments",
-			pkgPath: "github.com/mattermost/mattermost-server/server/public/plugin/checker/internal/test/valid",
+			pkgPath: "github.com/mattermost/mattermost/server/public/plugin/checker/internal/test/valid",
 			err:     "",
 		},
 		{
 			name:    "invalid comments",
-			pkgPath: "github.com/mattermost/mattermost-server/server/public/plugin/checker/internal/test/invalid",
+			pkgPath: "github.com/mattermost/mattermost/server/public/plugin/checker/internal/test/invalid",
 			expected: result{
 				Errors: []string{"internal/test/invalid/invalid.go:15:2: missing a minimum server version comment on method InvalidMethod"},
 			},
 		},
 		{
 			name:    "missing API interface",
-			pkgPath: "github.com/mattermost/mattermost-server/server/public/plugin/checker/internal/test/missing",
+			pkgPath: "github.com/mattermost/mattermost/server/public/plugin/checker/internal/test/missing",
 			err:     "could not find API interface",
 		},
 		{
 			name:    "non-existent package path",
-			pkgPath: "github.com/mattermost/mattermost-server/server/public/plugin/checker/internal/test/does_not_exist",
+			pkgPath: "github.com/mattermost/mattermost/server/public/plugin/checker/internal/test/does_not_exist",
 			err:     "could not find API interface",
 		},
 	}