build(node): add KOKORO_BUILD_ARTIFACTS_SUBDIR to env (#444)

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Source-Link: googleapis/synthtool@ba9918c

packages/google-cloud-redis/synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/nodejs-redis.git",
-        "sha": "4fa353781a580143cb244569642acd822c33e67e"
+        "sha": "ffc60152a6499099ff8a9ae54c6014455b8a93aa"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "89c849ba5013e45e8fb688b138f33c2ec6083dc5"
+        "sha": "ba9918cd22874245b55734f57470c719b577e591"
       }
     }
   ],