Fix GIT_GC_CHECK for multiple replicas (#490)

### Benefits

Asserting the value existence failed previously.

### Applicable issues

fixes #488

### Additional information

No unit tests possible as value is parsed as a secret and then into `app.ini`.

Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/490
Reviewed-by: justusbunsi <justusbunsi@noreply.gitea.com>
Co-authored-by: pat-s <patrick.schratz@gmail.com>
Co-committed-by: pat-s <patrick.schratz@gmail.com>

templates/gitea/config.yaml

@@ -25,10 +25,8 @@ stringData:
 
 {{- /* multiple replicas assertions */ -}}
 {{- if gt .Values.replicaCount 1.0 -}}
-  {{- if .Values.gitea.config.cron.GIT_GC_REPOS -}}
-    {{- if .Values.gitea.config.cron.GIT_GC_REPOS.enabled -}}
-      {{- fail "Invoking the garbage collector via CRON is not yet supported when running with multiple replicas. Please set 'GIT_GC_REPOS.enabled = false'." -}}
-    {{- end }}
+  {{- if (get (get .Values.gitea.config "cron.GIT_GC_REPOS") "ENABLED") -}}
+    {{- fail "Invoking the garbage collector via CRON is not yet supported when running with multiple replicas. Please set 'cron.GIT_GC_REPOS.enabled = false'." -}}
   {{- end }}
 
   {{- if eq (first .Values.persistence.accessModes) "ReadWriteOnce" -}}