EAMxx: use pack size 1 in valg build, to avoid false-positives from padding

Similar to what we do for FPE builds

Author: bartgol

components/eamxx/scripts/test_factory.py

@@ -156,6 +156,7 @@ def __init__(self, tas):
             "Release build where tests run through valgrind",
             [("CMAKE_BUILD_TYPE", "RelWithDebInfo"),
              ("EKAT_ENABLE_VALGRIND", "True"),
+             ("SCREAM_PACK_SIZE", "1"),
              ("SCREAM_TEST_MAX_THREADS", "2")],
             uses_baselines=False,
             on_by_default=False,