Update actions/upload-artifact@v6 -> v7

Author: dtolnay

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
       - run: cargo test --features float_roundtrip,arbitrary_precision --tests -- --skip ui --exact
       - run: cargo test --features raw_value --tests -- --skip ui --exact
       - run: cargo test --features unbounded_depth --tests -- --skip ui --exact
-      - uses: actions/upload-artifact@v6
+      - uses: actions/upload-artifact@v7
         if: matrix.os == 'ubuntu' && always()
         with:
           name: Cargo.lock