[release-16.0] Port two flaky test fixes #12603 and #12546

[rohit-nayak-ps]

Description

• Use atomic.Bool for fakesqldb behavior flags Use atomic.Bool for fakesqldb behavior flags #12603
• Flakes: Address Common Unit Test Races Flakes: Address Common Unit Test Races #12546

Related issues

#12603
#12546

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

[vitess-bot]

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