fix(@angular/build): ensure correct URL joining for prerender routes #9296

Job	Run time
build-e2e-windows	4m 44s
lint	1m 49s
build	4m 19s
test	3m 21s
Browser Compatibility Tests	3m 21s
publish-snapshots	3m 20s
e2e-windows (windows-2025, 22, npm, 0)	2m 57s
e2e-windows (windows-2025, 22, npm, 4)	2m 56s
e2e-windows (windows-2025, 22, esbuild, 1)	2m 57s
e2e-windows (windows-2025, 22, npm, 3)	2m 56s
e2e-windows (windows-2025, 22, npm, 5)	2m 57s
e2e-windows (windows-2025, 22, npm, 2)	2m 57s
e2e-windows (windows-2025, 22, npm, 1)	2m 57s
e2e-windows (windows-2025, 22, esbuild, 0)	2m 54s
e2e-windows (windows-2025, 22, esbuild, 5)	2m 52s
e2e-windows (windows-2025, 22, esbuild, 4)	2m 57s
e2e-windows (windows-2025, 22, esbuild, 2)	2m 56s
e2e-windows (windows-2025, 22, esbuild, 3)	2m 56s
e2e	1s
e2e-snapshots	1s
e2e-package-managers	1s
	56m 9s

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