fix(@angular/build): inject testing polyfills in Karma unit-test exec… #9426

Job	Run time
lint	2m 2s
build-e2e-windows	3m 43s
build	3m 18s
test	5m 10s
Browser Compatibility Tests	5m 9s
publish-snapshots	5m 7s
e2e-windows (windows-2025, 22, npm, 1)	4m 44s
e2e-windows (windows-2025, 22, npm, 5)	4m 45s
e2e-windows (windows-2025, 22, npm, 4)	4m 47s
e2e-windows (windows-2025, 22, npm, 2)	4m 44s
e2e-windows (windows-2025, 22, npm, 0)	4m 44s
e2e-windows (windows-2025, 22, npm, 3)	4m 44s
e2e-windows (windows-2025, 22, esbuild, 1)	4m 42s
e2e-windows (windows-2025, 22, esbuild, 2)	4m 46s
e2e-windows (windows-2025, 22, esbuild, 4)	4m 43s
e2e-windows (windows-2025, 22, esbuild, 5)	4m 45s
e2e-windows (windows-2025, 22, esbuild, 3)	4m 45s
e2e-windows (windows-2025, 22, esbuild, 0)	4m 47s
e2e-snapshots	1s
e2e-package-managers	1s
e2e	1s
	1h 21m 28s

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