Update actions/upload-artifact@v6 -> v7

Author: dtolnay

.github/workflows/ci.yml

@@ -41,7 +41,7 @@ jobs:
       - run: cargo test --workspace --exclude thiserror_no_std_test
       - run: cargo test --manifest-path tests/no-std/Cargo.toml
       - run: cargo test --no-default-features
-      - uses: actions/upload-artifact@v6
+      - uses: actions/upload-artifact@v7
         if: matrix.rust == 'nightly' && always()
         with:
           name: Cargo.lock