build: disable assistant_to_the_branch_manager on forks #9483

Job	Run time
lint	2m 0s
build	3m 21s
build-e2e-windows	3m 34s
publish-snapshots	10s
test	10s
Browser Compatibility Tests	11s
e2e-snapshots	1s
e2e	1s
e2e-package-managers	1s
e2e-windows	1s
	9m 30s

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