TableFilter: fix excluded RE listing

[shlomi-noach]

Description

Per #12317, this PR fixes the slice concatenation for excludeTableREs. While at it, adding more unit tests to validate expected behavior, and while at it, modernize the unit test file to use testify rather than "bare meta" golang tests.

Related Issue(s)

Fixes #12317

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[shlomi-noach]

ignoring the failures of onlineddl_vrepl and Upgrade Downgrade Testing Query Serving (Schema)