Improve string concat #192

Job	Run time
build (windows-latest, net7.0, x64)	5m 14s
build (windows-latest, net6.0, x64)	4m 59s
build (windows-latest, net5.0, x64)	5m 10s
build (windows-latest, netcoreapp3.1, x64)	5m 40s
build (ubuntu-latest, net7.0, x64)	1m 0s
build (ubuntu-latest, net6.0, x64)	1m 2s
build (ubuntu-latest, net5.0, x64)	45s
build (ubuntu-latest, netcoreapp3.1, x64)	57s
build (macos-13, net7.0, x64)	1m 37s
build (macos-13, net6.0, x64)	1m 26s
build (macos-13, net5.0, x64)	1m 16s
build (macos-13, netcoreapp3.1, x64)	1m 28s
build (windows-latest, net48, x64)	4m 14s
build (windows-latest, net48, x86)	3m 57s
build (windows-latest, net7.0, x86)	3m 47s
build (windows-latest, net6.0, x86)	10m 27s
build (windows-latest, net5.0, x86)	5m 57s
build (windows-latest, netcoreapp3.1, x86)	8m 27s
upload	1m 33s
	1h 8m 56s

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