(maint) acceptance tests: pin module versions

Pin puppetdb module to 7.14.0, otherwise inifile dependency is too new
for Puppet 6/Ruby 2.5.

Pin postgresql module to 8.4.0, otherwise apt dependency is too new for
Puppet 6/Ruby 2.5

acceptance/helper.rb

@@ -441,15 +441,8 @@ def get_package_version(host, version = nil)
   end
 
   def install_puppetdb_module(hosts, puppet_platform)
-    if test_config[:install_mode] == :upgrade_oldest
-      # Use custom branch of puppetlabs-postgres for puppet 6 agents with gpg keys updated for last module release that was puppet 6 compatible
-      on(hosts, 'curl -L https://github.com/puppetlabs/puppetlabs-postgresql/archive/refs/heads/backport-gpg-key.tar.gz --output /tmp/puppetlabs-postgresql')
-      on(hosts, 'puppet module install /tmp/puppetlabs-postgresql')
-      on(hosts, 'puppet module install puppetlabs-puppetdb --version 7.13.0')
-    else
-      # While we sort out a new puppetlabs-puppetdb module release, point to a branch that allows us to take the latest puppetlabs-postgresql module
-      on(hosts, 'puppet module install puppetlabs-puppetdb')
-    end
+    on(hosts, 'puppet module install puppetlabs-postgresql --version 8.3.0')
+    on(hosts, 'puppet module install puppetlabs-puppetdb --version 7.14.0')
   end
 
   def install_puppetdb(host, version=nil)