Auto merge of #1563 - lzutao:dummy-actions, r=RalfJung
Auto merge of #1563 - lzutao:dummy-actions, r=RalfJung

Add a dummy actions template to enable it on CI

I already had a complete template to transition from Travis and Appveyor.
Since actions will not run on repo haven't enabled it before.
I have this dummy template first to enable it on default branch.
We should address a few todo here, merge it and I will send another patch
to complete the migration.

rust-lang/miri,rust-lang/miri,rust-lang/miri,rust-lang/miri