Avoid kubelet warnings for imagePullSecret entries with empty names

[liggitt]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

Unfortunately, API validation permits imagePullSecret entries with empty Name fields (xref #99454 (comment)). The kubelet should skip those when computing pull secrets, rather than warning when the unnamed secret predictably cannot be fetched.

Does this PR introduce a user-facing change?

NONE

/cc @wojtek-t
/sig node

[k8s-ci-robot]

@liggitt: This issue is currently awaiting triage.

If a SIG or subproject determines this is a relevant issue, they will accept it by applying the triage/accepted label and provide further guidance.

The triage/accepted label can be added by org members by writing /triage accepted in a comment.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: liggitt

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• pkg/kubelet/OWNERS [liggitt]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[wojtek-t]

/lgtm

Thanks!

[fejta-bot]

/retest
This bot automatically retries jobs that failed/flaked on approved PRs (send feedback to fejta).

Review the full test history for this PR.

Silence the bot with an /lgtm cancel or /hold comment for consistent failures.