timeit: change default repeat to 5, instead of 3

Issue #28240: timeit now repeats the benchmarks 5 times instead of only 3 to
make benchmarks more reliable.
diff --git a/Lib/timeit.py b/Lib/timeit.py
index 0040efd..d40998c 100644
--- a/Lib/timeit.py
+++ b/Lib/timeit.py
@@ -59,7 +59,7 @@
 
 dummy_src_name = "<timeit-src>"
 default_number = 1000000
-default_repeat = 3
+default_repeat = 5
 default_timer = time.perf_counter
 
 _globals = globals