Update registry1.dso.mil/ironbank/opensource/debian/debian Docker tag to v12.6

This MR contains the following updates:

Package	Type	Update	Change
registry1.dso.mil/ironbank/opensource/debian/debian	ironbank-base	minor	12.5 -> 12.6
registry1.dso.mil/ironbank/opensource/debian/debian	final	minor	12.5 -> 12.6

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