Update GitHub Actions workflow

* Use `snapcore/action-build`

Signed-off-by: Daniel Llewellyn <diddledan@ubuntu.com>

Author: Daniel Llewellyn

.github/workflows/build-prs.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
-    - uses: jhenstridge/snapcraft-build-action@v1
+    - uses: snapcore/action-build@v1
       id: build
     - uses: diddlesnaps/snapcraft-review-tools-action@v1
       with: