Update mitre/heimdall-lite Docker tag to v2.8.8

This MR contains the following updates:

Package	Type	Update	Change
mitre/heimdall-lite	ironbank-docker	minor	2.6.47 -> 2.8.8
mitre/heimdall-lite		minor	2.6.47 -> 2.8.8
mitre/heimdall-lite	stage	minor	2.6.47 -> 2.8.8

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