Update _index.md (#3088)

# What this PR does
Fixed a typo in the line #93 (changed `doen't` to `doesn't`)

## Which issue(s) this PR fixes

## Checklist

- [ ] Unit, integration, and e2e (if applicable) tests updated
- [* ] Documentation added (or `pr:no public docs` PR label added if not
required)
- [ ] `CHANGELOG.md` updated (or `pr:no changelog` PR label added if not
required)

docs/sources/integrations/_index.md

@@ -90,7 +90,7 @@ will be sent to users.
 #### Heartbeat monitoring
 
 An OnCall heartbeat acts as a healthcheck for alert group monitoring. You can configure you monitoring to regularly send alerts
-to the heartbeat endpoint. If OnCall doen't receive one of these alerts, it will create an new alert group and escalate it
+to the heartbeat endpoint. If OnCall doesn't receive one of these alerts, it will create an new alert group and escalate it
 
 1. Go to Integration page and click **Three dots**
 1. Select **Heartbeat Settings**