deps: google-cloud-core 2.6.0 (#668)

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Author: suztomo

first-party-dependencies/pom.xml

@@ -62,7 +62,7 @@
  <protobuf.version>3.19.4</protobuf.version>
  <google.api-common.version>2.1.5</google.api-common.version>
  <google.common-protos.version>2.8.3</google.common-protos.version>
- <google.core.version>2.5.11</google.core.version>
+ <google.core.version>2.6.0</google.core.version>
  <google.auth.version>1.6.0</google.auth.version>
  <google.http-client.version>1.41.7</google.http-client.version>
  <google.oauth-client.version>1.33.3</google.oauth-client.version>