add a probe workflow for the artifact upload

The release takes four minutes to reach the upload and fails there on a
check the action makes before any request leaves the runner. The probe
asks the same questions in seconds: what the runner puts in the GITHUB_
names, whether a step-level env reaches a JS action at all, and which of
v3 and v4 gets an artifact through.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.gitea/workflows/probe-artifacts.yml

@@ -0,0 +1,70 @@
+# A throwaway workflow: it answers, in one run, what the release cannot ask
+# without building for four minutes first.
+#
+# Three questions. Whether a step-level env reaches a JS action at all or the
+# runner overwrites the GITHUB_ names with its own; whether this Gitea speaks
+# the v4 artifact protocol (ACTIONS_RESULTS_URL is the giveaway); and whether
+# the v3 action still gets its artifact through. Every upload is allowed to
+# fail, so a single run reports on all three rather than stopping at the first.
+#
+# Delete this file once the release works
+name: Probe the artifacts
+
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      - 'probe/**'
+
+defaults:
+  run:
+    shell: pwsh
+
+jobs:
+  probe:
+    runs-on: windows-x64
+
+    steps:
+      - name: Make a file to upload
+        run: |
+          New-Item -ItemType Directory -Force probe | Out-Null
+          'probe' | Out-File probe/probe.txt -Encoding utf8
+
+      # What the runner hands out on its own
+      - name: Show the environment as it comes
+        run: |
+          "server = [$env:GITHUB_SERVER_URL]"
+          "api    = [$env:GITHUB_API_URL]"
+          "results= [$env:ACTIONS_RESULTS_URL]"
+          "runtime= [$env:ACTIONS_RUNTIME_URL]"
+
+      # The same, with the substitution the release step makes. A run step is
+      # not a JS action, but if the name is overwritten even here, the answer is
+      # settled and nothing in the workflow can set it
+      - name: Show the environment with the substitution
+        env:
+          GITHUB_SERVER_URL: https://github.com
+        run: '"server = [$env:GITHUB_SERVER_URL]"'
+
+      - name: Upload with v4, plain
+        continue-on-error: true
+        uses: actions/upload-artifact@v4
+        with:
+          name: probe-v4-plain
+          path: probe/
+
+      - name: Upload with v4 and the substitution
+        continue-on-error: true
+        uses: actions/upload-artifact@v4
+        env:
+          GITHUB_SERVER_URL: https://github.com
+        with:
+          name: probe-v4-substituted
+          path: probe/
+
+      - name: Upload with v3
+        continue-on-error: true
+        uses: actions/upload-artifact@v3
+        with:
+          name: probe-v3
+          path: probe/