Fix OpenBLAS install script avoid GitHub API JSON parsing

[weimeng23]

Summary

This PR improves tools/extras/install_openblas.sh by avoiding the GitHub API call used to resolve the OpenBLAS tarball URL.

The previous implementation fetched release metadata from the GitHub API and parsed tarball_url with Python:

wget -qO- "https://api.github.com/repos/OpenMathLib/OpenBLAS/releases/tags/v${OPENBLAS_VERSION}" \
  | python3 -c 'import sys,json;print(json.load(sys.stdin)["tarball_url"])'

On some environments, especially machines with restricted network access, proxy issues, GitHub API rate limits, or temporary API failures, this command may return empty or non-JSON content. In that case, the script fails with an error like:

json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

Change

Instead of querying the GitHub API, this PR downloads the OpenBLAS release tarball directly from the stable tag archive URL:

https://github.com/OpenMathLib/OpenBLAS/archive/refs/tags/v${OPENBLAS_VERSION}.tar.gz

The script now uses the known OPENBLAS_VERSION value directly to construct the download URL.

Testing

Tested by running:

cd tools
bash extras/install_openblas.sh

Before this change, the script failed with:

json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

After this change, the script downloads the OpenBLAS tarball directly and proceeds to build/install OpenBLAS successfully.