fix(ci): downgrade artifact actions v4 -> v3 on main

Runner fetches the composite action from @main; main still had
upload-artifact@v4 which fails on Gitea (GHESNotSupportedError).
Brings the v3 action.yml from feature/python-rewrite-and-linux-migration.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/actions/local-ci-build/action.yml

@@ -282,7 +282,7 @@ runs:
     # ── Upload build artifacts on success ─────────────────────────────────────
     - name: Upload artifacts
       if: success() && inputs.skip-artifact != 'true'
-      uses: actions/upload-artifact@v4
+      uses: actions/upload-artifact@v3
       with:
         name: ${{ steps.invoke-ci.outputs.artifact-name }}
         path: ${{ steps.invoke-ci.outputs.artifact-path }}\
@@ -292,7 +292,7 @@ runs:
     # ── Upload diagnostic logs on failure ─────────────────────────────────────
     - name: Upload diagnostic logs on failure
       if: failure()
-      uses: actions/upload-artifact@v4
+      uses: actions/upload-artifact@v3
       with:
         name: build-logs-${{ github.sha }}
         path: ${{ steps.invoke-ci.outputs.artifact-path }}\*.log