Swap to setuptools>=77.0 licence specification (#15128)

PEP 639[^1] introduced a new way of specifying the licence information
of projects, both in the `pyproject.toml` metadata and in the resulting
`METADATA` object of the package.  Setuptools 77 (released in March
2025) both began accepting the new form and immediately deprecated the
old form.  We avoided moving to the new TOML keys in `pyproject.toml`
immediately because we didn't want to rely on a too-recent version of
the build toolchain, but given `setuptools`' development process, a
six-month delay seems about the right trade-off between supporting older
packages and not breaking on new releases.

The `License ::` trove classifiers in the metadata were simultaneously
deprecated as part of PEP 639, since the licence-expression form of the
metadata now serves that purpose in a more general and well-supported
manner.

[^1]: https://peps.python.org/pep-0639/

Author: jakelishman

pyproject.toml

@@ -1,12 +1,20 @@
 [build-system]
-requires = ["setuptools", "wheel", "setuptools-rust"]
+# We duplicate the `requires` in `requirements-dev.txt` as a
+# convenience for developers.
+requires = [
+    "setuptools>=77.0",
+    "setuptools-rust",
+]
 build-backend = "setuptools.build_meta"
 
 [project]
 name = "qiskit"
 description = "An open-source SDK for working with quantum computers at the level of extended quantum circuits, operators, and primitives."
 requires-python = ">=3.9"
-license = {text = "Apache 2.0"}
+license = "Apache-2.0"
+license-files = [
+    "LICENSE.txt",
+]
 authors = [
     { name = "Qiskit Development Team", email = "[email protected]" },
 ]
@@ -22,7 +30,6 @@ classifiers = [
     "Environment :: Console",
     "Intended Audience :: Developers",
     "Intended Audience :: Science/Research",
-    "License :: OSI Approved :: Apache Software License",
     "Operating System :: MacOS",
     "Operating System :: Microsoft :: Windows",
     "Operating System :: POSIX :: Linux",

releasenotes/notes/bump-setuptools-6e1d2c92924b4e61.yaml

@@ -0,0 +1,7 @@
+---
+other:
+  - |
+    When building or packaging Qiskit from source, the version of `setuptools` required is now at
+    least version 77.0 (released in March 2025).  This is to support the new license-metadata
+    specifications of `PEP 639 <https://peps.python.org/pep-0639/>`__.  This dependency is specified
+    in the build requirements, and so no manual action should be needed.

requirements-dev.txt

@@ -6,7 +6,10 @@
 # possible so it's easy to develop multiple packages from the same venv.
 
 # Build Rust directly
-setuptools
+#
+# The normative version of these is in `pyproject.toml`, and are included here
+# as a convenience for setting up a build/dev environment without isolation.
+setuptools>=77.0
 setuptools-rust
 
 # Style