gh-100538: Create a workflow for verifying bundled libexpat files

[illia-v]

Tags of libexpat releases are signed and GitHub runs a verification process on them.

I added a check of the verification status retrieved via GitHub's API. If the check succeeds, the script downloads a release source code and compares content of bundled files to the source.

Since a few lines are added to Modules/expat/expat_external.h, I moved them to the top of the file and the script skips them.

• Issue: Create a GitHub Actions workflow for verifying bundled libexpat files #100538

[sobolevn]

You don't need news for build tools :)

[illia-v]

@sobolevn I removed the news entry