Update registry1.dso.mil/ironbank/suse/bci/bci-base Docker tag to v15.6

This MR contains the following updates:

Package	Type	Update	Change
registry1.dso.mil/ironbank/suse/bci/bci-base	ironbank-base	minor	15.5 -> 15.6
registry1.dso.mil/ironbank/suse/bci/bci-base	final	minor	15.5 -> 15.6

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