[3.12] pythongh-126909: Fix running xattr tests on systems with lower limits (pythonGH-126930) (python#126964)

pythongh-126909: Fix running xattr tests on systems with lower limits (pythonGH-126930)

Modify the extended attribute tests to write fewer and smaller extended
attributes, in order to fit within filesystems with total xattr limit
of 1 KiB (e.g. ext4 with 1 KiB blocks).  Previously, the test would
write over 2 KiB, making it fail with ENOSPC on such systems.
(cherry picked from commit 2c0a21c)

Co-authored-by: Michał Górny <mgorny@gentoo.org>

Author: miss-islington

Lib/test/test_os.py

@@ -3478,10 +3478,10 @@ def _check_xattrs_str(self, s, getxattr, setxattr, removexattr, listxattr, **kwa
         xattr.remove("user.test")
         self.assertEqual(set(listxattr(fn)), xattr)
         self.assertEqual(getxattr(fn, s("user.test2"), **kwargs), b"foo")
-        setxattr(fn, s("user.test"), b"a"*1024, **kwargs)
-        self.assertEqual(getxattr(fn, s("user.test"), **kwargs), b"a"*1024)
+        setxattr(fn, s("user.test"), b"a"*256, **kwargs)
+        self.assertEqual(getxattr(fn, s("user.test"), **kwargs), b"a"*256)
         removexattr(fn, s("user.test"), **kwargs)
-        many = sorted("user.test{}".format(i) for i in range(100))
+        many = sorted("user.test{}".format(i) for i in range(32))
         for thing in many:
             setxattr(fn, thing, b"x", **kwargs)
         self.assertEqual(set(listxattr(fn)), set(init_xattr) | set(many))