relax MEMORY_USAGE_THRESHOLD in test to account for slightly increase…

…d mem from tracing (#18890)

* reset peak before trace mem

* increase test mem threshold to account for additional mem from trace

* add comments

datadog_checks_base/tests/base/utils/db/test_db_statements.py

@@ -277,7 +277,8 @@ def test_compute_derivative_rows_mem_usage(self):
         Make sure we minimize the temporary objects created when computing the derivative
         This test is skipped if tracemalloc is not available
         '''
-        MEMORY_USAGE_THRESHOLD = 7 * 1024 * 1024  # 7 MB
+        # The memory usage threshold takes tracing overhead into account
+        MEMORY_USAGE_THRESHOLD = 8 * 1024 * 1024  # 8 MB
 
         try:
             import tracemalloc