Add Python 3.13 to the default interpreter universe (#20851)

This adds Python 3.13 to the default interpreter universe, so that we're
more ready to hit the ground running when it is eventually released.

https://peps.python.org/pep-0719/ suggests the plan is 3.13.0 stable
release on 2024-10-01. This PR will flow into Pants 2.22.0. We won't be
releasing 2.22.0 before 2024-07-09 (12 weeks after 2.20.0, on
2024-04-16), so there's a bit of slack even if 2.21 and 2.22 take longer
than 6 weeks to get out the door.

It looks like we won't be perfectly ready, because there's a similar
lockfile issue to #20354 for Python 3.12: our lockfiles use pip 24.0
which apparently doesn't support Python 3.13 (needs
pypa/pip#12462). Thus, we'll need to regenerate
our lockfiles once there's a pex release with a pip release with
pypa/pip#12462. I've filed
#20852 to track this.

src/python/pants/backend/python/subsystems/setup.py

@@ -60,6 +60,7 @@ class PythonSetup(Subsystem):
         "3.10",
         "3.11",
         "3.12",
+        "3.13",
     ]
 
     _interpreter_constraints = StrListOption(