build(deps): bump actions/upload-artifact from 5 to 6

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>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -38,7 +38,7 @@ jobs:
       - uses: actions/setup-go@v6
       - run: make release
       - name: upload artifacts
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: release-${{ github.run_id }}
           path: release/*
@@ -91,7 +91,7 @@ jobs:
           slug: opencontainers/umoci
           files: ${{ env.COVERAGE }}
       - name: upload coverage
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: coverage-${{ runner.os }}-${{ github.job }}-${{ strategy.job-index }}
           path: ${{ env.GOCOVERDIR }}
@@ -126,7 +126,7 @@ jobs:
           slug: opencontainers/umoci
           files: ${{ env.COVERAGE }}
       - name: upload coverage
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: coverage-${{ runner.os }}-${{ github.job }}-${{ strategy.job-index }}
           path: ${{ env.GOCOVERDIR }}
@@ -175,7 +175,7 @@ jobs:
           slug: opencontainers/umoci
           files: ${{ env.COVERAGE }}
       - name: upload coverage
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: coverage-${{ runner.os }}-${{ github.job }}-${{ strategy.job-index }}
           path: ${{ env.GOCOVERDIR }}
@@ -198,7 +198,7 @@ jobs:
         run: |
           ./hack/ci-coverage.sh --merge="$GOCOVERDIR" --func coverage/*/
       - name: upload final coverage
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: coverage
           path: ${{ env.GOCOVERDIR }}