Add net462 targeting #300

Job	Run time
Test (ubuntu, net6.0)	1m 16s
Code Coverage	4m 31s
Test (macos, net6.0)	1m 7s
Build (ubuntu-latest, netstandard2.0)	17s
Build (ubuntu-latest, netstandard2.1)	25s
Build (ubuntu-latest, net6.0)	29s
Build (ubuntu-latest, net462)	15s
Build (windows-latest, netstandard2.0)	1m 23s
Build (windows-latest, netstandard2.1)	1m 41s
Build (windows-latest, net6.0)	1m 30s
Build (windows-latest, net462)	1m 49s
Build (macos-latest, netstandard2.0)	21s
Build (macos-latest, netstandard2.1)	30s
Build (macos-latest, net6.0)	23s
Build (macos-latest, net462)	28s
Pack	1m 12s
	17m 37s

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