scripts: imgtool: fix compression with encryption #2431

Job	Run time
environment (esp32, secureboot-sign-rsa2048,secureboot-sign-rsa3072,secureboot-sign-ec256,secureb...	1m 43s
environment (esp32, serialrecovery)	1m 43s
environment (esp32s2, secureboot-sign-rsa2048,secureboot-sign-rsa3072,secureboot-sign-ec256,secur...	1m 54s
environment (esp32s2, serialrecovery)	1m 26s
environment (esp32s3, secureboot-sign-rsa2048,secureboot-sign-rsa3072,secureboot-sign-ec256,secur...	1m 52s
environment (esp32s3, serialrecovery)	1m 33s
environment (esp32c3, secureboot-sign-rsa2048,secureboot-sign-rsa3072,secureboot-sign-ec256,secur...	1m 52s
environment (esp32c3, serialrecovery)	1m 35s
environment (esp32, multi-image,multi-boot, multi)	1m 28s
environment (esp32s3, multi-image,multi-boot, multi)	1m 26s
	16m 32s

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