Update Ironbank Docker tags to v15.7.3

This MR contains the following updates:

Package	Update	Change
ironbank/gitlab/gitlab-runner/gitlab-runner	minor	15.6.0 -> v15.7.3
ironbank/gitlab/gitlab-runner/gitlab-runner	minor	v15.6.0 -> v15.7.3
registry1.dso.mil/ironbank/gitlab/gitlab-runner/gitlab-runner	minor	v15.6.0 -> v15.7.3
registry1.dso.mil/ironbank/gitlab/gitlab-runner/gitlab-runner-helper	minor	v15.6.0 -> v15.7.3

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