fix(images): update docker.io/invoiceninja/invoiceninja docker tag to v5.8.15

Author: renovate[bot]

k8s/k8s-prod/workloads/work/invoiceninja/app/helmrelease-invoiceninja.yaml

@@ -27,7 +27,7 @@ spec:
     image:
       registry: docker.io
       repository: invoiceninja/invoiceninja
-      tag: 5.8.10@sha256:2ff5a43728062325cd77de3ad7e722648725b13409be325965f6511f03c0c164
+      tag: 5.8.15@sha256:59a283bb7fab29d432047264b12066de4f13eae78fb03f8f5126bcbf75c20570
     existingSecret: invoiceninja-secret
     updateStrategy:
       type: Recreate