fix(@angular/ssr): improve header validation logic #9918

Job	Run time
build-e2e-windows	2m 47s
build	1m 9s
lint	2m 3s
publish-snapshots	0s
test	-1s
Browser Compatibility Tests	-1s
e2e-package-managers	-1s
e2e	-1s
e2e-snapshots	-1s
e2e-windows (24, esbuild, 5)	12m 44s
e2e-windows (24, esbuild, 4)	11m 54s
e2e-windows (24, esbuild, 3)	12m 21s
e2e-windows (24, esbuild, 1)	11m 28s
e2e-windows (24, webpack, 0)	31m 47s
e2e-windows (24, webpack, 2)	15m 35s
e2e-windows (24, esbuild, 0)	11m 11s
e2e-windows (24, webpack, 1)	16m 3s
e2e-windows (24, webpack, 5)	12m 45s
e2e-windows (24, webpack, 3)	21m 21s
e2e-windows (24, webpack, 4)	16m 17s
e2e-windows (24, esbuild, 2)	12m 35s
	3h 11m 55s

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