chore(ci): bump docker/setup-buildx-action v3→v4, build-push-action v6→v7 (#71)

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: maxholman

.github/workflows/pr.yml

@@ -78,10 +78,10 @@ jobs:
           gh release download "$CROSS_VERSION" --repo cross-rs/cross --pattern 'cross-x86_64-unknown-linux-musl.tar.gz' -D /tmp
           tar xz -C ~/.cargo/bin cross < /tmp/cross-x86_64-unknown-linux-musl.tar.gz
 
-      - uses: docker/setup-buildx-action@v3
+      - uses: docker/setup-buildx-action@v4
 
       - name: Build and cache cross Docker image
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@v7
         with:
           context: .
           file: Dockerfile.cross-musl
@@ -122,10 +122,10 @@ jobs:
           gh release download "$CROSS_VERSION" --repo cross-rs/cross --pattern 'cross-x86_64-unknown-linux-musl.tar.gz' -D /tmp
           tar xz -C ~/.cargo/bin cross < /tmp/cross-x86_64-unknown-linux-musl.tar.gz
 
-      - uses: docker/setup-buildx-action@v3
+      - uses: docker/setup-buildx-action@v4
 
       - name: Build and cache cross Docker image
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@v7
         with:
           context: .
           file: Dockerfile.cross-musl