(maint) Install Puppet 7 from Puppet Core

Currently, Phoenix modules install Puppet 8 gems from Puppet Core, but
Puppet 7 gems from Rubygems. The logic currently used in Phoenix module
gemfiles to determine whether to install from Puppet Core differs
slightly from that used in the latest PDK (3.5.1) template, causing
authentication errors when attempting to install Puppet 7 gems.

The current workflow with the new PDK 3.5.1 gemfile logic attempts to
install Puppet 7 gems from Puppet Core without passing on the proper
credentials.

I attempted to bridge the gap with 1499ab9, but I misunderstood how Ruby
ingested variables from GitHub Actions.

This commit updates unit tests with released Puppet gems to use Puppet
Core gems for Puppet 7.

Author: mhashizume

.github/workflows/unit_tests_with_released_puppet_gem.yaml

@@ -17,10 +17,8 @@ jobs:
         include:
           - puppet_version: '7'
             ruby: '2.7'
-            puppet_forge_token: ${{ null }}
           - puppet_version: '8'
             ruby: '3.1'
-            puppet_forge_token: 'YES'
 
           - os: 'ubuntu-latest'
             os_type: 'Linux'
@@ -46,8 +44,8 @@ jobs:
           ruby-version: ${{ matrix.ruby }}
           bundler-cache: true
         env:
-          BUNDLE_RUBYGEMS___PUPPETCORE__PUPPET__COM: forge-key:${{ matrix.puppet_version != '7' && secrets.PUPPET_FORGE_TOKEN_PUBLIC || '' }}
-          PUPPET_FORGE_TOKEN: ${{ matrix.puppet_forge_token }}
+          BUNDLE_RUBYGEMS___PUPPETCORE__PUPPET__COM: forge-key:${{ secrets.PUPPET_FORGE_TOKEN_PUBLIC || '' }}
+          PUPPET_FORGE_TOKEN: 'YES'
 
       - name: Run unit tests
         run: bundle exec rake parallel_spec