ci: downgrade artifact actions to v3 for Gitea compatibility

upload-artifact@v4 and download-artifact@v4 require GitHub.com's
artifact backend and are not supported on Gitea Actions (GHES).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -129,7 +129,7 @@ jobs:
         run: nfpm pkg --packager rpm --target dist/
 
       - name: Upload RPM artifact
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: rpm-package
           path: dist/mcpctl-*.rpm
@@ -201,7 +201,7 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Download RPM artifact
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v3
         with:
           name: rpm-package
           path: dist/