Fix port configuration in sitegen:serve (#1010) #558

Job	Run time
checkstyle	39s
build	1m 52s
copyright	24s
shellcheck	17s
javadoc	1m 14s
spotbugs	2m 37s
cli/linux-amd64	2m 13s
tests/cli-linux	2m 26s
vscode-extension	56s
tests/cli-windows	3m 29s
cli/windows-amd64	3m 8s
tests/cli-functional-linux	3m 37s
cli/darwin-amd64	5m 59s
tests/cli-functional-windows	4m 49s
tests/archetype-linux	1m 39s
tests/archetype-windows	3m 6s
tests/linker-linux	1m 40s
tests/linker-windows	2m 44s
tests/misc-linux	2m 33s
tests/misc-windows	4m 28s
	49m 50s

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