fix(@angular/ssr): allow underscores in host validation #10102

Job	Run time
build	31s
build-e2e-windows	30s
lint	30s
e2e-windows	1s
Browser Compatibility Tests	1s
test	1s
e2e-snapshots	1s
publish-snapshots	1s
e2e	1s
e2e-package-managers	1s
	1m 38s

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