Update actions/upload-artifact@v5 -> v6

.github/workflows/ci.yml

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5158ea5..16d3882 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -37,7 +37,7 @@
         if: matrix.rust == 'nightly'
         shell: bash
       - run: cargo test
-      - uses: actions/upload-artifact@v5
+      - uses: actions/upload-artifact@v6
         if: matrix.os == 'ubuntu' && matrix.rust == 'nightly' && always()
         with:
           name: Cargo.lock