fix(@angular/build): inject testing polyfills in Karma unit-test exec… #9427

Job	Run time
lint	1m 55s
build	3m 46s
build-e2e-windows	4m 10s
test	4m 45s
Browser Compatibility Tests	4m 45s
publish-snapshots	4m 46s
e2e-windows (windows-2025, 22, npm, 1)	4m 22s
e2e-windows (windows-2025, 22, npm, 2)	4m 18s
e2e-windows (windows-2025, 22, npm, 0)	4m 21s
e2e-windows (windows-2025, 22, npm, 5)	4m 21s
e2e-windows (windows-2025, 22, esbuild, 1)	4m 22s
e2e-windows (windows-2025, 22, esbuild, 3)	4m 17s
e2e-windows (windows-2025, 22, npm, 3)	4m 18s
e2e-windows (windows-2025, 22, esbuild, 2)	4m 24s
e2e-windows (windows-2025, 22, esbuild, 4)	4m 19s
e2e-windows (windows-2025, 22, esbuild, 0)	4m 19s
e2e-windows (windows-2025, 22, esbuild, 5)	4m 22s
e2e-windows (windows-2025, 22, npm, 4)	4m 18s
e2e-package-managers	1s
e2e	1s
e2e-snapshots	1s
	1h 16m 11s

Provide feedback