fix(@angular/build): improve error handling in unit-test builder #1975

Job	Run time
build	28s
lint	2m 27s
build-e2e-windows	25s
e2e-windows	0s
test	0s
Browser Compatibility Tests	0s
publish-snapshots	0s
e2e-package-managers	0s
e2e	0s
e2e-snapshots	0s
	3m 20s

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