GitHub Actions artifacts don't preserve file permissions—all files
become 644 after upload/download. When packaged into release tarballs,
the oxia binary remained non-executable, causing permission denied
errors for users.

## Changes

- Added `--mode=a+x` flag to tar command in
`.github/workflows/release.yaml` to set execute permissions on all files
in the archive

```yaml
tar --mode=a+x -czf "../../release-assets/oxia-${PLATFORM}.tar.gz" *
```

This ensures the binary is executable immediately after extraction
without requiring manual `chmod +x`.

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<details>

<summary>Original prompt</summary>

> 
> ----
> 
> *This section details on the original issue you should resolve*
> 
> <issue_title>fixes: permission lost for binary release</issue_title>
> <issue_description>### Motivation
> 
> When I use the binary release of oxia. I met a permission issue. 
> 
> ```
> ➜  bin ./oxia standalone
> zsh: permission denied: ./oxia
> ```
> 
> plus, do I need to sign the released binary? </issue_description>
> 
> ## Comments on the Issue (you are @copilot in this section)
> 
> <comments>
> </comments>
> 


</details>



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- Fixes oxia-db/oxia#869

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---------
Co-authored-by: mattisonchao <74767115+mattisonchao@users.noreply.github.com>