Bump actions/upload-artifact from 5 to 6 (#61)

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v5...v6)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -69,7 +69,7 @@ jobs:
             cd ../obj_NOSIMD
         fi
         bash -- ../config-fermat.sh -cpu "0:$(( $(nproc --all) - 1 ))"
-    - uses: actions/upload-artifact@v5
+    - uses: actions/upload-artifact@v6
       if: always()
       with:
         name: ${{ matrix.os }}_${{ matrix.cc }}_mlucas
@@ -123,7 +123,7 @@ jobs:
             cd ../obj_NOSIMD
         fi
         bash -- ../config-fermat.sh
-    - uses: actions/upload-artifact@v5
+    - uses: actions/upload-artifact@v6
       if: always()
       with:
         name: ${{ matrix.os }}_${{ matrix.cc }}_singlethreaded_mlucas
@@ -366,7 +366,7 @@ jobs:
             cd ../obj_NOSIMD
         fi
         bash -- ../config-fermat.sh -cpu "0:$(( $(sysctl -n hw.ncpu) - 1 ))"
-    - uses: actions/upload-artifact@v5
+    - uses: actions/upload-artifact@v6
       if: always()
       with:
         name: ${{ matrix.os }}_mlucas
@@ -417,7 +417,7 @@ jobs:
             cd ../obj_NOSIMD
         fi
         bash -- ../config-fermat.sh
-    - uses: actions/upload-artifact@v5
+    - uses: actions/upload-artifact@v6
       if: always()
       with:
         name: ${{ matrix.os }}_singlethreaded_mlucas
@@ -545,7 +545,7 @@ jobs:
             cd ../obj_NOSIMD
         fi
         bash -- ../config-fermat.sh -cpu "0:$(( NUMBER_OF_PROCESSORS - 1 ))"
-    - uses: actions/upload-artifact@v5
+    - uses: actions/upload-artifact@v6
       if: always()
       with:
         name: ${{ matrix.os }}_${{ matrix.cc }}_mlucas