fix: webhook delivery content-type (#9823) (#10458)

* fix: webhook delivery content-type (#9823)

* style: indent

* Update packages/backend/src/queue/processors/WebhookDeliverProcessorService.ts

Co-authored-by: Acid Chicken (硫酸鶏) <root@acid-chicken.com>

* style: trailing comma

---------

Co-authored-by: syuilo <Syuilotan@yahoo.co.jp>
Co-authored-by: Acid Chicken (硫酸鶏) <root@acid-chicken.com>

packages/backend/src/queue/processors/WebhookDeliverProcessorService.ts

@@ -39,6 +39,7 @@ export class WebhookDeliverProcessorService {
 					'X-Misskey-Host': this.config.host,
 					'X-Misskey-Hook-Id': job.data.webhookId,
 					'X-Misskey-Hook-Secret': job.data.secret,
+					'Content-Type': 'application/json',
 				},
 				body: JSON.stringify({
 					hookId: job.data.webhookId,