Disable `Scheduled` workflow on forks #26

Job	Run time
Get Scarb versions	5s
test-forge-unit-and-integration (2.7.1)	21m 20s
test-forge-e2e (2.7.1)	19m 56s
test-forge-unit-and-integration (2.8.5)	25m 40s
test-cast (2.7.1)	13m 45s
test-forge-e2e (2.8.5)	20m 24s
test-forge-unit-and-integration (2.9.1)	29m 17s
test-cast (2.8.5)	17m 22s
test-forge-e2e (2.9.1)	21m 12s
test-forge-unit-and-integration (2.9.2)	29m 12s
test-cast (2.9.1)	18m 40s
test-forge-e2e (2.9.2)	21m 31s
test-cast (2.9.2)	18m 50s
notify_if_failed	0s
	4h 17m 14s

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