Increase the free spaces in CI

[tenzen-y]

What this PR does / why we need it:
I added a step to remove unnecessary files to avoid CI's "No space left on device" error.

Before:

Filesystem      Size  Used Avail Use% Mounted on
/dev/root        84G   54G   30G  65% /
tmpfs           3.4G  172K  3.4G   1% /dev/shm
...

After:

Filesystem      Size  Used Avail Use% Mounted on
/dev/root        84G   41G   43G  49% /
tmpfs           3.4G  172K  3.4G   1% /dev/shm
...

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Checklist:

• Docs included if any changes are user facing

[tenzen-y]

Recently, we are facing the "No space left on device" error in many times.

https://github.com/kubeflow/katib/actions/workflows/publish-trial-images.yaml

[tenzen-y]

This PR is ready for review. PTAL
/assign @andreyvelich @johnugeorge

[andreyvelich]

Thanks for the improvement @tenzen-y!
/lgtm

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

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[tenzen-y]

@kubeflow/wg-automl-leads Can you restart https://github.com/kubeflow/katib/actions/runs/4493555298/jobs/7904918734?pr=2131?