add riscv64 to JDK17 release pipeline

[sxa]

This will be formally discussed at the next PMC meeting before performing a release, but this change will allow us to be able to release a JDK17 on Linux/riscv64 which is believed to be in a good state now, and this will allow us to fully prep and test a release prior to shipping.

[github-actions]

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[gdams]

LGTM (once you've addressed Martijn's change)