gradle/actions GitHub action

Hi folks,

I just closed a dependabot PR to bump gradle actions from 5 to 6 and
told it to "ignore this version".

I initially held off an earlier proposed change since it arrived about
the same time as we learnt about the Trivy Compromise and the new
version wasn't in the updated ASF Infra whitelist of actions.

But there has also been discussion around the changed license terms
where the gradle-actions-caching component is no longer released under
open source. And some folks have questioned some of the terms in the
new license.

I suspect there will end up being no issue with using the new version,
but I thought I would give it time for further discussion to play out
since we are not in any urgent need to use the new version, and we
know of no security vulnerabilities with the current version. We can
easily just apply the proposed PR manually if we need.

But if anyone has dived into the issue in a little more depth please
feel free to have a discussion.

Cheers, Paul.