Reduced the garbage collection frequency in runtests.py.

tests/runtests.py

@@ -2,6 +2,7 @@
 import argparse
 import atexit
 import copy
+import gc
 import os
 import shutil
 import socket
@@ -53,6 +54,13 @@ warnings.filterwarnings(
     category=RemovedInDjango41Warning,
 )
 
+# Reduce garbage collection frequency to improve performance. Since CPython
+# uses refcounting, garbage collection only collects objects with cyclic
+# references, which are a minority, so the garbage collection threshold can be
+# larger than the default threshold of 700 allocations + deallocations without
+# much increase in memory usage.
+gc.set_threshold(100_000)
+
 RUNTESTS_DIR = os.path.abspath(os.path.dirname(__file__))
 
 TEMPLATE_DIR = os.path.join(RUNTESTS_DIR, 'templates')