Update build status badge in README.md

[medyagh]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind test
/kind failing-test
/kind feature
/kind flake

What this PR does / why we need it:
The Readme shows non-existing build badge from travis, changing it to show github action tests job instead
Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Release note:

[dims]

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dims, medyagh

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• OWNERS [dims]

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