Fix project.license field

Should be table according to https://peps.python.org/pep-0621/#license

pyproject.toml

@@ -11,7 +11,7 @@ dynamic = [
 ]
 description = "Utility package of the Quantum Technology group of RWTH Aachen"
 readme = "README.md"
-license = "GPL-3.0"
+license = { text = "GPL-3.0"}
 requires-python = ">= 3.8"
 authors = [
     { name = "Quantum Technology Group, RWTH Aachen University" },