ci: guard on the tag itself, not the release object

A tag can exist without a release (pushed by hand), and that still means
the version is taken. Checking the tag makes the failure say 'bump the
version' instead of surfacing a raw NuGet duplicate error.

.gitea/workflows/release.yml

@@ -36,6 +36,8 @@ jobs:
 
       # A published NuGet version can never be replaced, so refuse to re-run an
       # already released version instead of silently doing nothing.
+      # Checks the tag itself: a tag can exist without a release object (e.g. it
+      # was pushed by hand), and that still means the version is spoken for.
       - name: Refuse to release an existing version
         env:
           TOKEN: ${{ secrets.GITEA_TOKEN }}
@@ -44,9 +46,9 @@ jobs:
           TAG="v${{ steps.version.outputs.value }}"
           CODE=$(curl -s -o /dev/null -w '%{http_code}' \
             -H "Authorization: token $TOKEN" \
-            "${{ github.server_url }}/api/v1/repos/${{ github.repository }}/releases/tags/$TAG")
+            "${{ github.server_url }}/api/v1/repos/${{ github.repository }}/tags/$TAG")
           if [ "$CODE" = "200" ]; then
-            echo "::error::$TAG is already released. Bump <Version> in the csproj on dev, then merge again."
+            echo "::error::$TAG already exists — version ${{ steps.version.outputs.value }} is already released. Bump <Version> in src/CertifiEd.Client/CertifiEd.Client.csproj on dev, then merge into production again."
             exit 1
           fi