fix(@angular/build): correctly configure per-browser headless mode in… #2389

Job	Run time
lint	1m 55s
build-e2e-windows	20s
build	29s
e2e-windows	-1s
test	0s
Browser Compatibility Tests	0s
publish-snapshots	0s
e2e-package-managers	-1s
e2e-snapshots	-1s
e2e	-1s
	2m 40s

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