CI Benchmarking. Reduce runtime further as overhead appears to have risen. (#11189)

Summary:
We had miscalculated (not sure if I suddenly can’t count, or if there is something else going on), and need to leave more overhead to get the benchmarks to run reliably under 1 hour.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11189

Reviewed By: cbi42

Differential Revision: D43052045

Pulled By: ajkr

fbshipit-source-id: 3fe68432ed76a1f87d34129b0246e6b6a70a49f2

.circleci/config.yml

@@ -156,8 +156,8 @@ commands:
           environment:
             LD_LIBRARY_PATH: /usr/local/lib
             # How long to run parts of the test(s)
-            DURATION_RO: 400
+            DURATION_RO: 300
-            DURATION_RW: 600
+            DURATION_RW: 500
             # Keep threads within physical capacity of server (much lower than default)
             NUM_THREADS: 1
             MAX_BACKGROUND_JOBS: 4