CI improvements (#230)

- llvm artifacts search, download and extract now in `get-llvm` action 
- `get-emsdk` action - clone, install, activate emsdk, so we don't need
to build `revive-builder` for this
- switch workflows to new actions
- `concurrency` for remaining workflows (cancel run if new run is
triggered)
- `target_commitish` for main release, fixes release commit 
- Run release workflow in PR without creating a release if PR is labeled
with `release-test`

---------

Co-authored-by: cornholio <0@mcornholio.ru>
Co-authored-by: Alexander Theißen <alex.theissen@me.com>
Co-authored-by: xermicus <cyrill@parity.io>
Co-authored-by: xermicus <bigcyrill@hotmail.com>

.github/workflows/release-llvm.yml

@@ -8,6 +8,10 @@ on:
         required: true
         description: llvm version in "x.x.x" format, e.g. "18.1.8"
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 env:
   CARGO_TERM_COLOR: always