Update openpolicyagent/conftest Docker tag to v0.28.3

This MR contains the following updates:

Package	Type	Update	Change
openpolicyagent/conftest	ironbank-docker	patch	v0.28.2 -> v0.28.3
openpolicyagent/conftest		patch	v0.28.2 -> v0.28.3
openpolicyagent/conftest	stage	patch	v0.28.2 -> v0.28.3

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