fix(sizer-receiver): 🐛 add fsGroup to pod securityContext for PVC write access

Distroless nonroot container (UID 65534) needs matching fsGroup to write
to the PVC used for SQLite migrations.

Ref: IPCEICIS-8514

otc/dev.t09.de/stacks/garm/sizer-receiver/deployment.yaml

@@ -16,6 +16,8 @@ spec:
       labels:
         app: sizer-receiver
     spec:
+      securityContext:
+        fsGroup: 65534
       containers:
         - name: receiver
           image: edp.buildth.ing/devfw-cicd/forgejo-runner-sizer-receiver:latest