checksum/config already defined

This fixes:

```
Helm install failed for release prom/perses with chart [email protected]: error while running post render on files: map[string]interface {}(nil): yaml: unmarshal errors: line 30: mapping key "checksum/config" already defined at line 29
```

charts/perses/templates/statefulset.yaml

@@ -20,9 +20,10 @@ spec:
       labels:
         {{- include "perses.selectorLabels" . | nindent 8 }}
       annotations:
-        checksum/config: {{ include (print $.Template.BasePath "/config.yaml") . | sha256sum }}
         {{- if .Values.datasources }}
         checksum/config: {{ include (print $.Template.BasePath "/datasources.yaml") . | sha256sum }}
+        {{- else }}
+        checksum/config: {{ include (print $.Template.BasePath "/config.yaml") . | sha256sum }}
         {{- end }}
     spec:
       serviceAccountName: {{ include "perses.serviceAccountName" . }}
@@ -98,4 +99,4 @@ spec:
         - name: datasources
           configMap:
             name: {{ include "perses.fullname" . }}-datasources
-        {{- end }}
+        {{- end }}