fix: alternative route of getting latest Gitea version

Use a code.forgejo.org mirror instead of the GitHub API to not be
subject to rate limiting.

.forgejo/workflows/gitea-upgrade.yml

@@ -0,0 +1,36 @@
+#
+#
+# https://code.forgejo.org/forgejo/end-to-end/settings/actions
+#
+# secrets.MIRROR_TOKEN_GITEA
+#   https://code.forgejo.org/forgejo-mirror scope read:repository
+#
+
+on:
+  pull_request_target:
+  push:
+    branches:
+      - 'main'
+      - 'wip-gitea'
+
+jobs:
+  gitea_upgrade:
+    name: gitea upgrade
+    runs-on: lxc-bookworm
+    steps:
+      - uses: https://data.forgejo.org/actions/checkout@v4
+      - name: prepare upload
+        run: |
+          mkdir -p /tmp/forgejo-upload
+          touch /tmp/forgejo-upload/PLACEHOLDER
+      - uses: actions/upload-artifact@v3
+        with:
+          name: forgejo-dev
+          path: /tmp/forgejo-upload
+      - uses: ./.forgejo/prepare-end-to-end
+      - name: gitea upgrades
+        run: |
+            su forgejo -c "./end-to-end.sh test_gitea_upgrades ${{ secrets.MIRROR_TOKEN_GITEA }}"
+      - name: full logs
+        if: always()
+        run: su forgejo -c "./end-to-end.sh show_logs"