fix: use old license text (#1050)

Before moving to scikit-build-core, this was the contents of the
`License` field. Putting the entire contents of the license file here
breaks `importlib.metadata.metadata("iminuit")` (see
python/cpython#119650), and isn't needed - the
license file is stored in the wheel already, and the currently only
canonical location for license metadata is the trove classifiers. PEP
639, which is currently provisionally accepted and waiting support in
packaging, PyPI, etc, solves this by supporting SPDX license
expressions. But that's not ready yet.

(This is not critical, but a minor annoyance I hit while debugging)

pyproject.toml

@@ -9,7 +9,7 @@ version = "2.30.1"
 maintainers = [{ name = "Hans Dembinski", email = "[email protected]" }]
 readme = "README.rst"
 requires-python = ">=3.9"
-license = { file = "LICENSE" }
+license = { text = "MIT+LGPL" }
 classifiers = [
     "Development Status :: 5 - Production/Stable",
     "Intended Audience :: Science/Research",