build: disable assistant_to_the_branch_manager on forks #2704

Job	Run time
list	21s
workflow (modules-builder-tests)	1m 52s
workflow (devkit-core-tests)	1m 30s
workflow (build-cli)	1m 43s
workflow (build-unit-tests)	2m 23s
workflow (devkit-core-tests-rerun)	1m 34s
	9m 23s

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