Add some tests to clarify the "must-change-password" behavior (#30693)

Follow  #30472:

When a user is created by command line `./gitea admin user create`:

Old behavior before #30472: the first user (admin or non-admin) doesn't
need to change password.

Revert to the old behavior before #30472

main.go

@@ -42,7 +42,7 @@ func main() {
 		log.GetManager().Close()
 		os.Exit(code)
 	}
-	app := cmd.NewMainApp(Version, formatBuiltWith())
+	app := cmd.NewMainApp(cmd.AppVersion{Version: Version, Extra: formatBuiltWith()})
 	_ = cmd.RunMainApp(app, os.Args...) // all errors should have been handled by the RunMainApp
 	log.GetManager().Close()
 }