scripts: imgtool: fix compression with encryption #10

Job	Run time
environment (esp32, secureboot-sign-rsa2048,secureboot-sign-rsa3072,secureboot-sign-ec256,secureb...	1m 48s
environment (esp32, serialrecovery)	1m 28s
environment (esp32s2, secureboot-sign-rsa2048,secureboot-sign-rsa3072,secureboot-sign-ec256,secur...	1m 44s
environment (esp32s2, serialrecovery)	1m 25s
environment (esp32s3, secureboot-sign-rsa2048,secureboot-sign-rsa3072,secureboot-sign-ec256,secur...	1m 51s
environment (esp32s3, serialrecovery)	1m 36s
environment (esp32c3, secureboot-sign-rsa2048,secureboot-sign-rsa3072,secureboot-sign-ec256,secur...	1m 48s
environment (esp32c3, serialrecovery)	1m 26s
environment (esp32, multi-image,multi-boot, multi)	1m 31s
environment (esp32s3, multi-image,multi-boot, multi)	1m 43s
	16m 20s

Provide feedback