[3.12] gh-119070: Update test_shebang_executable_extension to always use non-installed version (GH-119846) (GH-120016)

gh-119070: Update test_shebang_executable_extension to always use non-installed version (GH-119846)
(cherry picked from commit 5c48eb0)

Author: miss-islington

Lib/test/test_launcher.py

@@ -719,9 +719,9 @@ def test_literal_shebang_invalid_template(self):
         )
 
     def test_shebang_executable_extension(self):
-        with self.script('#! /usr/bin/env python3.12') as script:
-            data = self.run_py([script])
-        expect = "# Search PATH for python3.12.exe"
+        with self.script('#! /usr/bin/env python3.99') as script:
+            data = self.run_py([script], expect_returncode=103)
+        expect = "# Search PATH for python3.99.exe"
         actual = [line.strip() for line in data["stderr"].splitlines()
                   if line.startswith("# Search PATH")]
         self.assertEqual([expect], actual)