Add net462 targeting #307

Job	Run time
Code Coverage	4m 36s
Build (ubuntu-latest, netstandard2.0)	25s
Test (ubuntu, net6.0)	1m 16s
Build (ubuntu-latest, netstandard2.1)	18s
Test (macos, net6.0)	55s
Build (ubuntu-latest, net6.0)	23s
Build (ubuntu-latest, net462)	14s
Build (windows-latest, netstandard2.0)	57s
Build (windows-latest, netstandard2.1)	1m 41s
Build (windows-latest, net6.0)	1m 33s
Build (windows-latest, net462)	2m 8s
Build (macos-latest, netstandard2.0)	21s
Build (macos-latest, netstandard2.1)	23s
Build (macos-latest, net6.0)	22s
Build (macos-latest, net462)	21s
Pack	1m 25s
	17m 18s

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