ci: drop unsupported --skip-existing from twine upload

Gitea's PyPI registry rejects twine's --skip-existing flag
(UnsupportedConfiguration), which failed every publish run. Remove it and
instead tolerate an "already exists" conflict in the shell, so dev (unique
.devN versions) always publishes and a main re-run of an existing release
is treated as success rather than a hard failure.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -74,8 +74,20 @@ jobs:
           TWINE_USERNAME: ${{ github.actor }}
           TWINE_PASSWORD: ${{ secrets.PACKAGE_REGISTRY_TOKEN || secrets.GITHUB_TOKEN }}
         run: |
-          uvx twine upload \
+          # Gitea's PyPI registry does not support twine's --skip-existing, so
+          # we run a plain upload and tolerate an "already exists" conflict in
+          # the shell (dev versions are unique per run, so this only bites a
+          # main re-run of an already-published release).
+          set +e
+          out=$(uvx twine upload \
             --repository-url "${{ github.server_url }}/api/packages/${{ github.repository_owner }}/pypi" \
             --non-interactive \
-            --skip-existing \
-            dist/*
+            --verbose \
+            dist/* 2>&1)
+          code=$?
+          echo "$out"
+          if [ $code -ne 0 ] && echo "$out" | grep -qiE "already exist|conflict|409"; then
+            echo "::notice::Version already published — treating as success."
+            exit 0
+          fi
+          exit $code