Bump upload-artifact to v7 and download-artifact to v8

Fix Node.js 20 deprecation warnings in the release workflow.
Actions will be forced to Node.js 24 starting June 2, 2026.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: yahonda

.github/workflows/release.yml

@@ -23,7 +23,7 @@ jobs:
       - name: Build gem
         run: gem build ruby-plsql.gemspec
       - name: Upload gem artifact
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v7
         with:
           name: gem-cruby
           path: "*.gem"
@@ -39,7 +39,7 @@ jobs:
       actions: read
     steps:
       - name: Download CRuby gem
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           name: gem-cruby
       - name: Set up Ruby