Skip vulnerability scans for the alpine and pause images

[ialidzhikov]

How to categorize this PR?

/kind enhancement

What this PR does / why we need it:
The PR:

• excludes alpine and pause images from vulnerability scans
• updates alpine to 3.18.4

Which issue(s) this PR fixes:
N/A

Special notes for your reviewer:
The PR depends on gardener/ci-infra#990.

Release note:

Vulnerability scans are disabled for the alpine and pause images as the corresponding containers are not accessible from outside of the K8s clusters and not interacted with from other containers or other systems.

The following image is updated:
- `eu.gcr.io/gardener-project/3rd/alpine`: 3.15.8 -> 3.18.4

[gardener-prow]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[ialidzhikov]

/approve

[gardener-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ialidzhikov

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Needs approval from an approver in each of these files:

• OWNERS [ialidzhikov]

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[dimitar-kostadinov]

/lgtm

[gardener-prow]

LGTM label has been added.

Git tree hash: e2adff705dc0323f590f6a11c07e2738816b3aa5

[dimitar-kostadinov]

/retest