chore(tests): bump default docker test image to 8.8-m03

[nkaradzhov]

Description

Describe your pull request here

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Checklist

• Does npm test pass with this change (including linting)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?

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Note

Low Risk
Primarily a test-environment version bump plus small typing/cleanup changes; risk is limited to potential test behavior differences in the newer Redis 8.8 milestone image.

Overview
Updates the CI Redis version matrix and all package TestUtils.createFromConfig defaults from 8.8-m02 to 8.8-m03, so tests run against the newer 8.8 milestone image by default.

Also includes minor test-utility TypeScript hygiene fixes (sentinel test util import/type tightening, removing stray characters, var→let/const, ignoring unused params, and narrowing parseFirstKey args to unknown).

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