Fix flaky performance test

Ensure URL encoding takes enough time so that cached version is measurably 10x faster

Author: mrfaizal

tests/unit/gapic/test_routing_header.py

@@ -90,8 +90,8 @@ def test__urlencode_param(key, value, expected):
 def test__urlencode_param_caching_performance():
     import time
 
-    key = "key" * 100
-    value = "value" * 100
+    key = "key" * 10000
+    value = "value" * 10000
     # time with empty cache
     start_time = time.perf_counter()
     routing_header._urlencode_param(key, value)