Fix shellcheck failure in cluster/test-e2e.sh

[k-toyoda-pi]

What type of PR is this?
/kind cleanup

What this PR does / why we need it:
Fix shellcheck failure of cluster/test-e2e.sh

shellcheck detects the following failure.

In ./cluster/test-e2e.sh line 29:
TEST_ARGS="$@"
          ^--^ SC2124: Assigning an array to a string! Assign as array, or use * instead of @ to concatenate.

TEST_ARGS is only used in echo just after the line as far as I have checked.
So, this PR removes TEST_ARGS variable and changes echo line.

Which issue(s) this PR fixes:
Ref #72956

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

/sig testing
/priority backlog

[k-toyoda-pi]

/retest

[BenTheElder]

/lgtm
/approve

[k-toyoda-pi]

/assign @spiffxp
for approval

[oomichi]

/lgtm

[spiffxp]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: BenTheElder, k-toyoda-pi, spiffxp

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Needs approval from an approver in each of these files:

• cluster/OWNERS [spiffxp]
• hack/OWNERS [BenTheElder,spiffxp]

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