[release-3.5] Fix error in pull-etcd-release-tests when running in Prow

[joshjms]

Ref: kubernetes/test-infra#32754
Continuation of #20168
Partial backport of #19305

Rename the input "IMAGE" to "TEST_IMAGE" to avoid clashing with the environment variable from the Prow infrastructure.

Results in pj-on-kind

% '/home/prow/go/src/github.com/etcd-io/etcd/scripts/test_images.sh'
a92a0d16d13e6ac3add6d08bb8edb7b7b8541bc07ac21804ffb3f134862c638d
Succesfully tested etcd local image v3.5.99-amd64
Correct Architecture v3.5.99-amd64
Correct Architecture v3.5.99-arm64
Correct Architecture v3.5.99-ppc64le
Correct Architecture v3.5.99-s390x
test_etcd
'release_tests' completed at Mon Jul  7 09:39:51 UTC 2025
SUCCESS
+ EXIT_VALUE=0
+ set +o xtrace
Cleaning up after docker in docker.
================================================================================
Cleaning up after docker
Stopping Docker: dockerProgram process in pidfile '/var/run/docker-ssd.pid', 1 process(es), refused to die.
================================================================================
Done cleaning up after docker in docker.

/cc @ivanvc @abdurrehman107

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[abdurrehman107]

Just out of curiosity why are we changing it to TEST_IMAGE from IMAGE?

[jmhbnz]

LGTM - Thanks @joshjms

[ivanvc]

Just out of curiosity why are we changing it to TEST_IMAGE from IMAGE?

@abdurrehman107, refer to #19305

[ivanvc]

LGTM. Thanks, @joshjms.

[k8s-ci-robot]

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