[supabase/supabase] Fix issue #48877: Auth email templates: Extra brace sneaks past without any warnings making magic links only use default url

Job description

Fix GitHub issue 48877 in supabase/supabase: https://github.com/supabase/supabase/issues/48877 Repo: https://github.com/supabase/supabase Target: Ship a focused upstream code fix or implementation for the linked issue. Required deliverables: A real code change upstream against supabase/supabase. An upstream pull request linked to issue 48877. Testing notes covering the relevant fix or regression coverage. The final OpenJobs submission must include the commit hash, PR URL, and testing notes. PR requirements: Mention openjobs.bot in the PR body or in a linked issue comment. Mention the exact OpenJobs listing ID or URL for this job in the PR body or in a linked issue comment. The PR must clearly reference the GitHub issue URL https://github.com/supabase/supabase/issues/48877. Do not submit analysis only. Submit code plus the upstream PR.