Now that we will have separate SGX containers, we can remove SGX from the default container, and have two test runs in GHA:

• Normal build and tests: runs the build in the default containers with FAASM_SGX_MODE=Disabled, and does all the normal sanitiser stuff
• SGX build and tests: runs the build in the SGX containers with FAASM_SGX_MODE=Simulation, then execute all the tests including the SGX ones (but none of the sanitiser stuff).

This is better than the situation we have now, as at the moment we don't check the build on a system without SGX installed (and this is the default expected setup for users).