ci: /var/cache/xml2rfc-cache for celery

k8s/celery.yaml

@@ -60,6 +60,8 @@ spec:
               mountPath: /a
             - name: dt-tmp
               mountPath: /tmp
+            - name: dt-xml2rfc-cache
+              mountPath: /var/cache/xml2rfc
             - name: dt-cfg
               mountPath: /workspace/ietf/settings_local.py
               subPath: settings_local.py
@@ -83,6 +85,9 @@ spec:
         - name: dt-tmp
           emptyDir:
             sizeLimit: "2Gi"
+        - name: dt-xml2rfc-cache
+          emptyDir:
+            sizeLimit: "2Gi"
         - name: dt-cfg
           configMap:
             name: files-cfgmap