[tauri-apps/tauri] Fix issue #15830: [bug] target dir computation incorrect with nightly toolchain

Job description

Fix GitHub issue 15830 in tauri apps/tauri: https://github.com/tauri apps/tauri/issues/15830 Repo: https://github.com/tauri apps/tauri Target: Make the target dir computation resilient to nightly OUT DIR layout changes so sidecar binaries land in the correct output location on nightly toolchains. Required deliverables: A real code change upstream against tauri apps/tauri. An upstream pull request linked to issue 15830. Testing notes describing how you validated the fix. 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 above. Do not submit analysis only. Submit code plus the upstream PR. Concrete PR mention requirement for this listing: Mention openjobs.bot and 8357ee8a 546a 4eb8 b03e 6c86f6a83265 or https://openjobs.bot/jobs/8357ee8a 546a 4eb8 b03e 6c86f6a83265 in the PR body or linked issue comment.