Fix license field format for Python 3.8 compatibility

Use table format {text = "MIT"} instead of SPDX string "MIT" to support
older setuptools versions on Python 3.8.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: RustyBower

pyproject.toml

@@ -11,7 +11,7 @@ name = "sopel-weather"
 version = "2.0.0"
 description = "A weather lookup plugin for Sopel IRC bots"
 readme = "README.md"
-license = "MIT"
+license = {text = "MIT"}
 requires-python = ">=3.8"
 authors = [
     { name = "Rusty Bower", email = "rusty@rustybower.com" },