[azure-cli] cannot specifiy bicep version when using installBicep; it will aways use latest

[jurjenoskam]

When setting installBicep to true, it is not possible to specify which Bicep version will be installed; it will always use whatever latest happens to point at when the container is built.

This means you can end up with a team of people developing against different Bicep versions, and as there have been some behavioral changes (and even the odd breaking change here and there) between Bicep versions in the past, this is something I'd like to avoid.

I've submitted #1227 as a suggested fix.