gh: import and adapt rust workflow

Two modifications have been done:

- Restrict the build on push to the main branch only, similar to what
  was done in commit 4da53c3 ("github: restrict builds on push to the
  main branch")

- Change the working directory to ./virtme_ng_init, because the root
  directory is now different.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>

Author: matttbe

virtme_ng_init/.github/workflows/rust.yml renamed to .github/workflows/rust.yml

@@ -2,6 +2,8 @@ name: Rust
 
 on:
   push:
+    branches:
+      - main
   pull_request:
 
 env:
@@ -12,6 +14,10 @@ jobs:
 
     runs-on: ubuntu-latest
 
+    defaults:
+      run:
+        working-directory: ./virtme_ng_init
+
     steps:
     - uses: actions/checkout@v3
     - name: Coding style