chore(tests): bump default docker test image to 8.8.0

[nkaradzhov]

Summary

• Bump default docker test image from custom-26235535976-debian to 8.8.0 (official 8.8 GA tag on redislabs/client-libs-test)
• Update CI matrix entry for 8.8 accordingly

Test plan

• CI green across node 20/22 × redis 7.4/8.2/8.4/8.8 matrix

🤖 Generated with Claude Code

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Note

Low Risk
Test and CI configuration only; no runtime library or application behavior changes.

Overview
Switches Redis 8.8 integration testing from a one-off custom-26235535976-debian image to the published 8.8.0 tag on redislabs/client-libs-test.

The GitHub Actions test matrix uses 8.8.0 for the 8.8 row, and every package TestUtils.createFromConfig default (defaultDockerVersion.tag) is updated the same way (bloom, client, sentinel, entraid, json, search, test-utils, time-series).

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