fix(jupyterhub): correct data type of new cpu_guarantee

[themightychris]

Description

Correct syntax in #3507

[github-actions]

The following changes will be applied to the production Kubernetes cluster upon merge.

BE AWARE this may not reveal changes that have been manually applied to the cluster getting undone—applying manual changes to the cluster should be avoided.

jupyterhub, hub, Deployment (apps) has changed:
...
          hub.jupyter.org/network-access-proxy-api: "true"
          hub.jupyter.org/network-access-proxy-http: "true"
          hub.jupyter.org/network-access-singleuser: "true"
        annotations:
          checksum/config-map: ecf5268b9d342e8ab7c99ede7cbfde395133c574e9a4b24e25c2e825968e8311
-         checksum/secret: 9a395c20c97d0e1430511c3a659beccc80b2f8736c4be9ed578ae0031e23d178
+         checksum/secret: 748d3ab2f9a030f641afa2dd5145c08aeb19b9dd83c2ac9b7a4dbd5d5e6873e0
      spec:
        tolerations:
          - effect: NoSchedule
            key: hub.jupyter.org/dedicated
            operator: Equal
...
jupyterhub, hub, Secret (v1) has changed:
...
    name: hub
  data:
    hub.config.ConfigurableHTTPProxy.auth_token: 'REDACTED # (64 bytes)'
    hub.config.CryptKeeper.keys: 'REDACTED # (64 bytes)'
    hub.config.JupyterHub.cookie_secret: 'REDACTED # (64 bytes)'
-   values.yaml: '-------- # (11561 bytes)'
+   values.yaml: '++++++++ # (11559 bytes)'
  type: Opaque