fix(@angular/build): ensure karma polyfills reporter factory returns … #8507

Job	Run time
lint	1m 23s
build-e2e-windows	1m 26s
build	1m 24s
e2e-windows	1s
publish-snapshots	1s
test	1s
e2e	1s
Browser Compatibility Tests	1s
e2e-package-managers	1s
e2e-snapshots	1s
	4m 20s

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