Specify correct supported puppet version, 8.x only #89

Job	Run time
Nightly / Puppet8 gem on Ruby 3.1 on Linux	1m 54s
Nightly / Puppet8 gem on Ruby 3.1 on Windows	15m 46s
Released / Puppet8 gem on Ruby 3.1 on Linux	19s
Released / Puppet8 gem on Ruby 3.1 on macOS	26s
Released / Puppet8 gem on Ruby 3.1 on Windows	1m 24s
	19m 49s

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