chore(test): fix prechecks in e2e

[nevermarine]

Description

Align the custom e2e precheck label filter parser with Ginkgo label filter syntax by treating ! as a negation prefix.

Why do we need it, and what problem does it solve?

The e2e precheck loader parsed negated labels differently from Ginkgo. Ginkgo uses !Slow, while the custom precheck filter expected ~Slow. As a result, when running tests with --label-filter='!Slow', Ginkgo excluded slow specs correctly, but the precheck loader treated !Slow as a required label name, collected no matching specs, and skipped all non-common prechecks.

This change removes that mismatch and makes precheck selection consistent with the actual Ginkgo run.

What is the expected result?

1. Run e2e tests with go tool ginkgo --label-filter='!Slow'.
2. Verify slow specs are excluded by Ginkgo.
3. Verify prechecks required by the remaining specs are still detected and executed.
4. Verify only unrelated specs are skipped, while non-common prechecks are no longer dropped incorrectly.

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: test
type: fix
summary: "Make e2e precheck label parsing compatible with Ginkgo negated label filters."
impact_level: low