ci: fix test workflow

The `test` workflow only fetched the latest commit and thus only tested
that one instead of the entire pull request.

Signed-off-by: Benno Lossin <lossin@kernel.org>

Author: BennoLossin

.github/workflows/ci.yml

@@ -68,6 +68,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: ${{github.event.pull_request.commits}}
+          ref: ${{github.event.pull_request.head.sha}}
       - uses: dtolnay/rust-toolchain@nightly
         with:
           components: rust-src