build(java): use ENABLE_FLAKYBOT env variable (#1238)

Kokoro job config now supports both environment variables during this migration period.

Source-Author: Jeff Ching <chingor@google.com>
Source-Date: Thu Aug 12 10:10:27 2021 -0700
Source-Repo: googleapis/synthtool
Source-Sha: ff01716e16d2c6e87eaf87197b753ac9fcbbed5d
Source-Link: googleapis/synthtool@ff01716

.kokoro/nightly/integration.cfg

@@ -22,7 +22,7 @@ env_vars: {
 }
 
 env_vars: {
-  key: "ENABLE_BUILD_COP"
+  key: "ENABLE_FLAKYBOT"
   value: "true"
 }
 

synth.metadata

@@ -11,7 +11,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-bigquerystorage.git",
-        "sha": "93a0eaeb520b803e56d61087f2ffb4f6beaa83ed"
+        "sha": "cb2bc2ff90ad828b7749068ff9a7c38bdf92cfb5"
       }
     },
     {
@@ -42,7 +42,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "1a2878d6909dd10ca4e3c1b5943d6622e996054e"
+        "sha": "ff01716e16d2c6e87eaf87197b753ac9fcbbed5d"
       }
     }
   ],