fix(@schematics/angular): silently skip when the build target already… #9326

Job	Run time
build	3m 1s
lint	2m 5s
build-e2e-windows	3m 4s
e2e-snapshots	1s
Browser Compatibility Tests	1s
test	1s
publish-snapshots	1s
e2e-package-managers	1s
e2e	1s
e2e-windows	1s
	8m 17s

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