Use env GITEA_RUNNER_REGISTRATION_TOKEN as global runner token (#32946)

Fix #23703

When Gitea starts, it reads GITEA_RUNNER_REGISTRATION_TOKEN
or GITEA_RUNNER_REGISTRATION_TOKEN_FILE to add registration token.

routers/web/shared/actions/runners.go

@@ -136,9 +136,8 @@ func RunnerResetRegistrationToken(ctx *context.Context, ownerID, repoID int64, r
 		ctx.ServerError("ResetRunnerRegistrationToken", err)
 		return
 	}
-
 	ctx.Flash.Success(ctx.Tr("actions.runners.reset_registration_token_success"))
-	ctx.Redirect(redirectTo)
+	ctx.JSONRedirect(redirectTo)
 }
 
 // RunnerDeletePost response for deleting a runner