[release-4.18] gitmodules: track rhcos-4.18 branch

[mike-nguyen]

Start tracking the rhcos-4.18 branch of fedora-coreos-config as a part of branching 4.18

[marmijo]

/lgtm

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: marmijo, mike-nguyen

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[mike-nguyen]

/label backport-risk-assessed
/label cherry-pick-approved

[mike-nguyen]

/test rhcos-9-build-test-qemu

[openshift-ci]

@mike-nguyen: The following tests 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/scos-9-build-test-metal	d8d5eae	link	true	/test scos-9-build-test-metal
ci/prow/scos-9-build-test-qemu	d8d5eae	link	true	/test scos-9-build-test-qemu

Full PR test history. Your PR dashboard.

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