.ostc-ci: fix detection of conflicting caching options

The intent was to detect when we both have public cache and accept the
FSL EULA but the shell logic was just broken. Instead of writing:

    if command; then ... fi

I wrote:

    if [ command ]; then ... fi

And nothing in the system noticed, because, separately, none of the
scripts seem to execute with `set -e` in effect. That will be addressed
separately.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>
Change-Id: I6e87261b831ced591466139dbf10316610d4a879
13 jobs for !80 with fix/grep-test-snafu in 44 minutes and 10 seconds (queued for 4 seconds)
detached
Status Job ID Name Coverage
  Compliance
passed #20405
dco

00:00:03

 
  Build
passed #20417
large-disk
freertos-armv5

00:03:49

passed #20408
large-disk
linux-qemu-arm

00:15:17

passed #20409
large-disk
linux-qemu-arm64

00:15:27

passed #20406
large-disk
linux-qemu-x86

00:15:18

passed #20407
large-disk
linux-qemu-x86_64

00:15:17

passed #20411
large-disk
linux-seco-imx8mm-c61

00:17:40

passed #20410
large-disk
linux-seco-intel-b68

00:17:19

passed #20412
large-disk
linux-stm32mp1-av96

00:28:48

passed #20416
large-disk
zephyr-96b-avenger

00:03:37

passed #20415
large-disk
zephyr-96b-nitrogen

00:03:43

passed #20414
large-disk
zephyr-qemu-cortex-m3

00:03:49

passed #20413
large-disk
zephyr-qemu-x86

00:03:29