TST: install pip 24.1b1 or later when on Python 3.13t

Earlier pip releases do not recognize the free-threading ABI flag.

Author: dnicolodi

tests/conftest.py

@@ -10,11 +10,13 @@
 import shutil
 import subprocess
 import sys
+import sysconfig
 import tempfile
 import warnings
 
 from venv import EnvBuilder
 
+import packaging.version
 import pytest
 
 import mesonpy
@@ -77,13 +79,23 @@ def tmp_path_session(tmp_path_factory):
 class VEnv(EnvBuilder):
     def __init__(self, env_dir):
         super().__init__(symlinks=True, with_pip=True)
+
         # This warning is mistakenly generated by CPython 3.11.0
         # https://github.com/python/cpython/pull/98743
         with warnings.catch_warnings():
             if sys.version_info[:3] == (3, 11, 0):
                 warnings.filterwarnings('ignore', 'check_home argument is deprecated and ignored.', DeprecationWarning)
             self.create(env_dir)
 
+        # Free-threaded Python 3.13 requires pip 24.1b1 or later.
+        if sysconfig.get_config_var('Py_GIL_DISABLED'):
+            # importlib.metadata is not available on Python 3.7 and
+            # earlier, however no-gil builds are available only for
+            # Python 3.13 and later.
+            import importlib.metadata
+            if packaging.version.Version(importlib.metadata.version('pip')) < packaging.version.Version('24.1b1'):
+                self.pip('install', '--upgrade', 'pip >= 24.1b1')
+
     def ensure_directories(self, env_dir):
         context = super().ensure_directories(env_dir)
         # Store the path to the venv Python interpreter. There does