tooling: set project.license to {text="MIT"} instead of a whole file

Short names for standard licenses are preferred per
https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license
(and look better on PyPI).

pyproject.toml

@@ -7,7 +7,7 @@ name = "gcalcli"
 dynamic = ["version"]
 requires-python = ">= 3.8"
 readme = "README.md"
-license = { file = "LICENSE" }
+license = { text = "MIT" }
 authors = [
   { name = "Eric Davis", email = "[email protected]" },
   { name = "Brian Hartvigsen", email = "[email protected]" },