tests: fix: increase snapshot memory threshold in MemoryMonitor

Increases the threshold for snapshot tests to remove flakiness in tests
that snapshot VMs with many vCPUs.

Signed-off-by: Riccardo Mancini <mancio@amazon.com>

Author: Manciukic

tests/host_tools/memory.py

@@ -47,7 +47,7 @@ def __init__(
         self,
         vm,
         threshold_booted=5 << 20,
-        threshold_snapshot=6 << 20,
+        threshold_snapshot=7 << 20,
         threshold_restored=5 << 20,
         period_s=0.01,
     ):