Downweight fuzztest. (#4006)

It's causing starvation problems in one of our deployments.

Author: jonathanmetzman

src/clusterfuzz/_internal/cron/fuzzer_and_job_weights.py

@@ -50,8 +50,10 @@
 }
 
 ENGINE_WEIGHTS = {
-    'libFuzzer': 1.0,
     'afl': 1.0,
+    'centipede': 1.0,
+    'googlefuzztest': 0.1,
+    'libFuzzer': 1.0,
     'honggfuzz': 0.2,
 }