fix(plugin-release): remove invalid --json flag from gh pr create

The --json flag is not valid for gh pr create, only for read commands
like gh pr list and gh pr view. This was causing the release workflow
to fail with 'unknown flag: --json' in the Create PR step.

The PR number is correctly retrieved on the line after via gh pr list,
so no other change was needed.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/plugin-release.yaml

@@ -354,8 +354,7 @@ jobs:
               --title "release: v${VERSION}" \
               --body "$BODY" \
               --base main \
-              --head "release/v${VERSION}" \
-              --json number --jq '.number'
+              --head "release/v${VERSION}"
             # Pull the number again to handle both create and pre-existing cases
             OPEN_PR=$(gh pr list --base main --head "release/v${VERSION}" --state open --json number --jq '.[0].number' 2>/dev/null)
           else