pull-image-with-system-assigned-mi.bicep needs updates on the role assignment

[felixtsem5]

In the following file, the scope of the roleAssignment is set to containerApp, which means that we are granting the managed identity of the containerApp with the AcrPull permission to itself (and not the ACR).

set-image-with-system-assigned-mi.bicep

[felixtsem5]

@Ajsalemo