ci: update set-output to new form

reference:
https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

.github/workflows/release.yml

@@ -14,7 +14,7 @@ jobs:
       - uses: actions/checkout@v3
       - id: matrix
         run: |
-          echo '::set-output name=s6_arch::'$(cut -f1 conf/toolchains | sed -z '$ s/\n$//' | jq -R -s -c 'split("\n")')
+          echo s6_arch=$(cut -f1 conf/toolchains | sed -z '$ s/\n$//' | jq -R -s -c 'split("\n")') >> "$GITHUB_OUTPUT"
 
       - run: |
           . conf/versions