grafana: Update to 11.5.5

The legacy alerting feature (which we never used) has been deprecated
for a long time and removed in Grafana 11.  The corresponding
configuration block must be removed from the config file or Grafana will
not start.

grafana/grafana.yaml

@@ -76,6 +76,8 @@ spec:
         - mountPath: /etc/grafana/provisioning/datasources
           name: datasources
           readOnly: true
+        - mountPath: /tmp
+          name: tmp
         - mountPath: /run/secrets/grafana
           name: secrets
           readOnly: true
@@ -96,6 +98,9 @@ spec:
       - name: grafana
         persistentVolumeClaim:
           claimName: grafana
+      - name: tmp
+        emptyDir:
+          medium: Memory
       - name: secrets
         secret:
           secretName: grafana