gh-143309: fix test_execve_env_concurrent_mutation_with_fspath_posix buildbot failure

Author: picnixz

Lib/test/test_os/test_os.py

@@ -2627,6 +2627,8 @@ def test_execve_invalid_env(self):
     # See https://github.com/python/cpython/issues/137934 and the other
     # related issues for the reason why we cannot test this on Windows.
     @unittest.skipIf(os.name == "nt", "POSIX-specific test")
+    @unittest.skipUnless(unix_shell and os.path.exists(unix_shell),
+                        "requires a shell")
     def test_execve_env_concurrent_mutation_with_fspath_posix(self):
         # Prevent crash when mutating environment during parsing.
         # Regression test for https://github.com/python/cpython/issues/143309.
@@ -2648,9 +2650,9 @@ def __len__(self): return 1
             def keys(self): return KEYS
             def values(self): return VALUES
 
-        args = [sys.executable, '-c', "print({message!r})"]
+        args = [{unix_shell!r}, '-c', 'echo \"{message!s}\"']
         os.execve(args[0], args, MyEnv())
-        """.format(message=message)
+        """.format(unix_shell=unix_shell, message=message)
 
         # Use '__cleanenv' to signal to assert_python_ok() not
         # to do a copy of os.environ on its own.