Fix the test script to be compatible with older Pythons

scripts/check_zipapp.py

@@ -1,10 +1,21 @@
 import subprocess
 import sys
 
-proc = subprocess.run(
+# This code needs to support all versions of Python we test against
+proc = subprocess.Popen(
     [sys.executable] + sys.argv[1:],
-    capture_output=True,
+    stdout=subprocess.PIPE,
+    stderr=subprocess.PIPE,
 )
+proc.wait()
 
-if proc.returncode != 0:
-    assert b"does not support python" in proc.stderr
+out = proc.stdout.read()
+err = proc.stderr.read()
+
+if proc.returncode == 0:
+    print(out)
+elif b"does not support python" in err:
+    print(err)
+else:
+    print(err)
+    raise SystemExit("Failed")