Update registry1.dso.mil/ironbank/opensource/alpinelinux/alpine Docker tag to v3.21

This MR contains the following updates:

Package	Type	Update	Change
registry1.dso.mil/ironbank/opensource/alpinelinux/alpine	ironbank-base	minor	3.20 -> 3.21
registry1.dso.mil/ironbank/opensource/alpinelinux/alpine	final	minor	3.20 -> 3.21

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