Modify some test cases to prevent them from allocating too much

mjtest/test/exec_tests.py

@@ -153,7 +153,10 @@ class JavaExecTest(BasicSyntaxTest):
     def _check_hash_sum(self, file: str, hash_sum_file: str) -> bool:
         old_hash = ""
         with open(hash_sum_file, "r") as f:
-            old_hash = f.readline().strip()
+            try:
+                old_hash = f.readline().strip()
+            except UnicodeDecodeError:
+                _LOG.exception("Decoding a hash sum for java output caching failed")
         return self._hash_sum_for_file(file) == old_hash
 
     def _hash_sum_for_file(self, file: str) -> str: