[TF-M] Open CI Does Not Cover ITS/PS Access Flash Tests on MUSCA_B1

Hi,

I'm sorry to inform you that ITS/PS access flash on MUSCA_B1 could not be covered on Open CI for the time being. Because the flash on MUSCA_B1 board in Open CI is broken, we temporarily use RAM_FS as workaround. This issue will be fixed ASAP. We'll keep following and inform you with further updates.

Sorry for any inconvenience!

BR, Xinyu