Fix minor issue in docs for creating a Cronjob for rotate the GCP access tokens

[rbrunan]

Description of your changes

This is only a documentation change, with the current guide, I obtained an error running the Job:

kubectl logs -n crossplane cred-sync-001-tc4xk                                                                                                   ─╯
/bin/bash: -c: line 3: syntax error near unexpected token `('

This was fixed with the proposed change.

How has this code been tested

I tested the proposed change in a test GCP cluster running k8s v1.24.11.

[Upbound-CLA]

All committers have signed the CLA.

[jeanduplessis]

Thank you for the fix @rbrunan