puppetlabs-acl: tests cannot be run with beaker 4.0 compatability issues

Before a puppet-agent can be promoted into PE, it runs through PEZ for some validation in the agent CI pipeline. The acl module tests have been failing since the release of beaker 4.0. Here is an example of the test run failure in CI:

https://jenkins-master-prod-1.delivery.puppetlabs.net/job/forge-windows_puppetlabs-acl_intn-sys-generic-smoke_puppet-agent/PLATFORM=windows2008r2-64default.a,UNNEEDED=UNNEEDED,WORKER_LABEL=beaker/738/console

The failure is being caused by the fact that beaker 4.0 is being installed, and subsequently the beaker-rspec gem cannot be installed, because it hasn't declared compatibility with beaker 4.0. (serverspec is a dependency of the beaker-rspec gem, and isn't being found because beaker-rspec isn't being installed).

I thought this might be a simple matter of pinning beaker in the acl module's Gemfile to 3.x, but ethan pointed out that the Gemfile is automatically generated via another process:

https://github.com/puppetlabs/puppetlabs-acl/pull/129

I'd prefer not to risk breaking anything further, so I'm ticketing this issue and hoping someone with better context can address this.