toolbox: update docker-credential-gcr to v2.1.5

BUG=b/235120580

Change-Id: Ibe1c9c36bf39230ecff0c773a915f28b03552c61
Reviewed-on: https://cos-review.googlesource.com/c/cos/tools/+/33543
Reviewed-by: Sam Kunz <samkunz@google.com>
Cloud-Build: GCB Service account <228075978874@cloudbuild.gserviceaccount.com>
Reviewed-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
Tested-by: Arnav Kansal <rnv@google.com>
diff --git a/src/cmd/toolbox/Dockerfile b/src/cmd/toolbox/Dockerfile
index 3594639..8d20d0c 100644
--- a/src/cmd/toolbox/Dockerfile
+++ b/src/cmd/toolbox/Dockerfile
@@ -10,8 +10,8 @@
 
 ARG TARGETARCH
 
-RUN cd $(mktemp -d) && curl -L -O "https://github.com/GoogleCloudPlatform/docker-credential-gcr/releases/download/v2.1.2/docker-credential-gcr_linux_$TARGETARCH-2.1.2.tar.gz" && \
-    tar xvf "docker-credential-gcr_linux_$TARGETARCH-2.1.2.tar.gz" && \
+RUN cd $(mktemp -d) && curl -L -O "https://github.com/GoogleCloudPlatform/docker-credential-gcr/releases/download/v2.1.5/docker-credential-gcr_linux_$TARGETARCH-2.1.5.tar.gz" && \
+    tar xvf "docker-credential-gcr_linux_$TARGETARCH-2.1.5.tar.gz" && \
     mv docker-credential-gcr /usr/bin/ && rm -r $(pwd)
 
 # Install the Google Cloud SDK.