scripts: flash_script.sh: Check the MAGISKBIN variable before constructing the environment #4540

Job	Run time
Build Magisk artifacts	12m 55s
Test building on windows-latest	9m 9s
Test building on ubuntu-latest	3m 41s
Test aosp_cf_x86_64_phone	5m 5s
Test aosp_cf_x86_64_phone_pgagnostic	5m 58s
Test API 23 (x86)	10m 18s
Test API 23 (x86_64)	3m 20s
Test API 24 (x86)	2m 14s
Test API 24 (x86_64)	2m 43s
Test API 25 (x86)	1m 54s
Test API 25 (x86_64)	2m 53s
Test API 26 (x86)	3m 15s
Test API 26 (x86_64)	2m 59s
Test API 27 (x86)	3m 42s
Test API 27 (x86_64)	3m 53s
Test API 28 (x86)	3m 30s
Test API 28 (x86_64)	3m 42s
Test API 29 (x86)	3m 22s
Test API 29 (x86_64)	3m 10s
Test API 30 (x86)	5m 23s
Test API 30 (x86_64)	3m 32s
Test API 31 (x86_64)	3m 38s
Test API 32 (x86_64)	3m 46s
Test API 33 (x86_64)	3m 58s
Test API 34 (x86_64)	3m 46s
Test API 35 (x86_64)	4m 2s
	1h 55m 48s

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