Publish to Modrinth with Node instead of Python

actions/setup-python can only install Python on GitHub's Ubuntu images,
so it fails on this runner's job image ("version 3.12 ... was not found
for this operating system"). Every Gitea runner has Node, since it runs
JavaScript actions, so port the publisher to a dependency-free Node
script (fetch/FormData/Blob) and drop the setup step. Behaviour is
unchanged.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

.gitea/workflows/modrinth.yml

@@ -25,11 +25,6 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Set up Python
-        uses: actions/setup-python@v5
-        with:
-          python-version: "3.12"
-
       - name: Publish to Modrinth
         env:
           TAG: ${{ inputs.tag }}
@@ -37,4 +32,5 @@ jobs:
           SERVER_URL: ${{ github.server_url }}
           REPO: ${{ github.repository }}
           MODRINTH_TOKEN: ${{ secrets.MODRINTH_TOKEN }}
-        run: python .gitea/scripts/publish_modrinth.py
+        # Node is always available on Gitea runners (it runs JavaScript actions).
+        run: node .gitea/scripts/publish_modrinth.mjs