Update capg 1.8.0

[barbacbd]

Vendor Cluster API Provider GCP version 1.8.0.

https://github.com/kubernetes-sigs/cluster-api-provider-gcp/tree/v1.8.0

[barbacbd]

/cc @r4f4
/cc @bfournie

[barbacbd]

/label platform/google

[openshift-ci]

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[r4f4]

/lgtm

[openshift-ci]

@barbacbd: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/e2e-aws-ovn-single-node	ae1f68b	link	false	/test e2e-aws-ovn-single-node

Full PR test history. Your PR dashboard.

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