bpo-44860: Update test_sysconfig for posix_user platlib (GH-28235)

Update test_sysconfig.test_user_similar() for the posix_user scheme:
"platlib" doesn't use sys.platlibdir.

Lib/test/pythoninfo.py

@@ -96,6 +96,7 @@ def collect_sys(info_add):
         'maxunicode',
         'path',
         'platform',
+        'platlibdir',
         'prefix',
         'thread_info',
         'version',

Lib/test/test_sysconfig.py

@@ -296,7 +296,17 @@ def test_user_similar(self):
                 base = base.replace(sys.base_prefix, sys.prefix)
             if HAS_USER_BASE:
                 user_path = get_path(name, 'posix_user')
-                self.assertEqual(user_path, global_path.replace(base, user, 1))
+                expected = global_path.replace(base, user, 1)
+                # bpo-44860: platlib of posix_user doesn't use sys.platlibdir,
+                # whereas posix_prefix does.
+                if name == 'platlib':
+                    # Replace "/lib64/python3.11/site-packages" suffix
+                    # with "/lib/python3.11/site-packages".
+                    py_version_short = sysconfig.get_python_version()
+                    suffix = f'python{py_version_short}/site-packages'
+                    expected = expected.replace(f'/{sys.platlibdir}/{suffix}',
+                                                f'/lib/{suffix}')
+                self.assertEqual(user_path, expected)
 
     def test_main(self):
         # just making sure _main() runs and returns things in the stdout

Misc/NEWS.d/next/Tests/2021-09-08-13-01-37.bpo-44860.qXd0kx.rst

@@ -0,0 +1,2 @@
+Update ``test_sysconfig.test_user_similar()`` for the posix_user scheme:
+``platlib`` doesn't use :data:`sys.platlibdir`. Patch by Victor Stinner.