spec-test-script: Make case_last_words larger (#3651)

The current size is usually too small to contain useful info for post mortem investigations.

tests/wamr-test-suites/spec-test-script/all.py

@@ -247,7 +247,7 @@ def test_case(
                 if verbose_flag:
                     print(output, end="")
                 else:
-                    if len(case_last_words) == 16:
+                    if len(case_last_words) == 1024:
                         case_last_words.pop(0)
                     case_last_words.append(output)