fix: incident.io config typo

Signed-off-by: Hélia Barroso <helia_barroso@hotmail.com>

pkg/alertmanager/testdata/incidentio_configs_for_supported_versions.golden

@@ -1,6 +1,6 @@
 receivers:
 - name: ""
-  incidentio_config:
+  incidentio_configs:
   - url: http://example.com
     alert_source_token: token123
 templates: []

pkg/alertmanager/testdata/incidentio_configs_with_http_authorization.golden

@@ -1,6 +1,6 @@
 receivers:
 - name: ""
-  incidentio_config:
+  incidentio_configs:
   - http_config:
       authorization:
         type: Bearer

pkg/alertmanager/types.go

@@ -120,7 +120,7 @@ type receiver struct {
 	JiraConfigs       []*jiraConfig       `yaml:"jira_configs,omitempty"`
 	RocketChatConfigs []*rocketChatConfig `yaml:"rocketchat_configs,omitempty"`
 	MattermostConfigs []*mattermostConfig `yaml:"mattermost_configs,omitempty"`
-	IncidentioConfigs []*incidentioConfig `yaml:"incidentio_config,omitempty"`
+	IncidentioConfigs []*incidentioConfig `yaml:"incidentio_configs,omitempty"`
 }
 
 type webhookConfig struct {