databases/py-pymssql: Update to 2.1.5

Changes since 2.1.4:

• Revert deprecation.
• Support Python-3.8. Update tests for Python-3.8 compatibility.
• Use correct language level for building Cython extension.
• Fix FreeTDS version checks. Add check for version 7.4.
• Use Github Actions for building wheels for Linux, macOS and Windows.
• Drop bundled FreeTDS-0.95 binaries.
• Unless some critical bug is discovered, this will be the last release with Python2 support.

PR: 270891
Reported by: You-Wei Cheah
Approved by: ports@thelanman.net (maintainer timeout, 16 days)