build: swap new buck audit steps into github actions

.github/workflows/buck2-audit.yaml

@@ -0,0 +1,37 @@
+name: Buck2 audit
+on:
+  pull_request:
+    branches: [main]
+    types: [opened, synchronize, labeled, unlabeled]
+
+jobs:
+  buck2-test:
+    name: Buck2 Audit
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install Nix
+        uses: DeterminateSystems/nix-installer-action@v4
+      - name: Run the Magic Nix Cache
+        uses: DeterminateSystems/magic-nix-cache-action@v2
+      - uses: actions/checkout@v3
+      - name: Prepare Buck2 audit args from labels
+        id: prepare_args
+        run: |
+          ARGS=""
+          cat <<EOF > labels.json
+          ${{ toJSON(github.event.pull_request.labels.*.name) }}
+          EOF
+          for LABEL in dashboard consent core; do
+            case "$LABEL" in
+              dashboard|consent)
+                ARGS+=" //apps/$LABEL:audit"
+                ;;
+              core)
+                ARGS+=" //core/api:audit"
+                ;;
+            esac
+          done
+          echo "Prepared args: $ARGS"
+          echo "args=$ARGS" >> "$GITHUB_OUTPUT"
+      - name: Buck2 test
+        run: nix develop -c buck2 test ${{ steps.prepare_args.outputs.args }}