Use puppet 6 nightlies and increase timeout limit

[carabasdaniel]

No description provided.

[codecov-io]

Codecov Report

Merging #373 (8763f67) into main (081baf9) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #373   +/-   ##
=======================================
  Coverage   62.89%   62.89%           
=======================================
  Files           7        7           
  Lines         857      857           
=======================================
  Hits          539      539           
  Misses        318      318           

Impacted Files	Coverage Δ
lib/puppet_litmus/rake_helper.rb	74.14% <100.00%> (ø)

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[carabasdaniel]

PR with test results here: https://github.com/puppetlabs/puppetlabs-testing/runs/1734154323?check_suite_focus=true