Fix release workflow display names and license badge

[LeonidElkin]

Summary

Clean up release workflow naming and fix the license badge shown in the README.

Changes

• Add an explicit run-name to the release workflow:
  • manual TestPyPI runs are shown as Release TestPyPI;
  • tag-based PyPI runs are shown as Release <tag> PyPI.
• Replace the dynamic GitHub license shield with a static MIT badge.

Notes

GitHub already recognizes the repository LICENSE file as MIT. The INVALID label came from the README badge provider, not from the actual license file.

The workflow naming change applies to future release workflow runs only.