test(api): adjust error in negative memory test

This is because guest memory is backed by anon
private mapping in a regular case.

Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>

tests/integration_tests/functional/test_api.py

@@ -392,7 +392,7 @@ def test_api_machine_config(uvm_plain):
     test_microvm.api.machine_config.patch(mem_size_mib=bad_size)
 
     fail_msg = re.escape(
-        "Invalid Memory Configuration: Cannot resize memfd file: Custom { kind: InvalidInput, error: TryFromIntError(()) }"
+        "Invalid Memory Configuration: Cannot create mmap region: Out of memory (os error 12)"
     )
     with pytest.raises(RuntimeError, match=fail_msg):
         test_microvm.start()