[GR-44300] Ignore stderr when comparing against expected output.

PullRequest: graalpython/2640

Author: ansalond

graalpython/com.oracle.graal.python.test/src/tests/test_patched_pip.py

@@ -84,7 +84,7 @@ def run_venv_pip_install(self, package, extra_env=None):
 
         def run_test_fun(self):
             code = "import patched_package; print(patched_package.test_fun())"
-            out = subprocess.getoutput(f"{self.venv_python} -c '{code}'").strip()
+            out = subprocess.check_output([self.venv_python, '-c', code], universal_newlines=True).strip()
             return out
 
         def test_pip_launcher(self):