Update registry1.dso.mil/ironbank/bitnami/postgres/postgresql11 Docker tag to v11.18.0

This MR contains the following updates:

Package	Type	Update	Change
registry1.dso.mil/ironbank/bitnami/postgres/postgresql11	ironbank-base	minor	11.17.0 -> 11.18.0
registry1.dso.mil/ironbank/bitnami/postgres/postgresql11	final	minor	11.17.0 -> 11.18.0

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