Skip tests that makes assumptions about String memory layout

Author: msimacek

graalpython/com.oracle.graal.python.test/src/tests/unittest_tags/test_unicode.txt

@@ -92,6 +92,7 @@
 *graalpython.lib-python.3.test.test_unicode.UnicodeTest.test_partition
 *graalpython.lib-python.3.test.test_unicode.UnicodeTest.test_printable_repr
 *graalpython.lib-python.3.test.test_unicode.UnicodeTest.test_printing
+*graalpython.lib-python.3.test.test_unicode.UnicodeTest.test_raiseMemError
 *graalpython.lib-python.3.test.test_unicode.UnicodeTest.test_replace
 *graalpython.lib-python.3.test.test_unicode.UnicodeTest.test_replace_id
 *graalpython.lib-python.3.test.test_unicode.UnicodeTest.test_replace_overflow

graalpython/lib-python/3/test/test_unicode.py

@@ -2302,6 +2302,8 @@ def test_expandtabs_optimization(self):
         s = 'abc'
         self.assertIs(s.expandtabs(), s)
 
+    # Makes assumptions about memory consumption of strings
+    @support.impl_detail(graalvm=False)
     def test_raiseMemError(self):
         if struct.calcsize('P') == 8:
             # 64 bits pointers