Keep prereleases in draft until release assets finish uploading (#54716)

## Why

Prereleases were published before their assets finished uploading, exposing incomplete releases.

## What changed

Create new prereleases as drafts, matching stable releases, and publish them only after all asset uploads succeed. Publishing a draft emits a `published` event rather than a `prereleased` event.

GitOrigin-RevId: 0d1c52038bb9b7beb4b5b9bf52f0ef4c3734de61

.github/workflows/rust-release.yml

@@ -1775,13 +1775,10 @@ jobs:
             --prerelease="$PRERELEASE"
           )
           if [[ "$exists" == false ]]; then
-            # Prereleases must be created directly to keep prereleased events.
-            draft=true
-            if [[ "$PRERELEASE" == true ]]; then
-              draft=false
-            fi
+            # Keep stable releases and prereleases private until all uploads succeed.
+            # Publishing a draft emits published rather than prereleased events.
             gh release create "$GITHUB_REF_NAME" "${release_args[@]}" \
-              --draft="$draft" --verify-tag --latest=false
+              --draft=true --verify-tag --latest=false
           fi
 
           mapfile -d '' assets < <(find dist -type f -print0 | sort -z)