Simplify CI - no need to list every embassy_* example explicitly

[bjoernQ]

It's easy to forget to add an example to CI (I always forget that) - so instead of checking each embassy_* example separately use --example=embassy*. That means we need to follow the convention of prefixing embassy examples with embassy_ which we already do

This might result in checking some examples multiple times (we do that already) I guess it's better for maintenance

Also, this changes from check to build to also verify the linker step

Some examples had other problems which are fixed, too

[bjoernQ]

Not sure if we really want this. I especially don't like the naming convention for the Xtensa examples needing the embassy-executor-interrupt

[bjoernQ]

Given the lack of activity here and the fact that CI might need a more radical rewrite .... closing this

I still think we need a more fool-proof way of checking examples ideally without listing them in the CI workflow