ci(release): upload into an existing release instead of creating a second one

.github/workflows/release.yaml

@@ -177,16 +177,23 @@ jobs:
         run: cd archives && sha256sum * > checksums.txt && cat checksums.txt
 
       # Draft, like goreleaser's `release.draft: true`; a prerelease suffix on
-      # the tag marks it prerelease, like `prerelease: auto`.
+      # the tag marks it prerelease, like `prerelease: auto`. `gh release
+      # create` is not idempotent: on a tag that already has a release it
+      # creates a second, untagged one and exits 0, so upload into the
+      # existing release instead.
       - name: Create draft release
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           GH_REPO: ${{ github.repository }}
         run: |
           prerelease=()
           case "$GITHUB_REF_NAME" in *-*) prerelease=(--prerelease) ;; esac
-          gh release create "$GITHUB_REF_NAME" --draft --generate-notes --title "$GITHUB_REF_NAME" \
-            "${prerelease[@]}" archives/*
+          if gh release view "$GITHUB_REF_NAME" >/dev/null 2>&1; then
+            gh release upload "$GITHUB_REF_NAME" --clobber archives/*
+          else
+            gh release create "$GITHUB_REF_NAME" --draft --generate-notes --title "$GITHUB_REF_NAME" \
+              "${prerelease[@]}" archives/*
+          fi
 
   # Build + push multi-arch Docker images on Linux (where the Docker daemon
   # lives), reusing the cgo linux binaries from the linux build jobs.