[release-17.0] Tablet throttler: fix race condition by removing goroutine call (#14179)

[shlomi-noach]

Backport of #14179 into release-17.0

Description

Per #14178, the function throttler.refreshMySQLInventory() should run on same goroutine as the select clause.

A note about testing: this of course would have been caught by race detection. We have a followup PR that make a lot of refactoring to the throttler code, and adds sufficient unit testing to validate the changes and to catch race conditions.

This PR is a one line extract from the followup PR, and without the unit testing. The reasoning is that the refactor is a post-v18 change, while the fix in this PR should be backported to v18, v17 and v16, which cannot support the many changes implied by the unit testing. And so this PR does not include those tests.

Said followup PR is #14181.

Related Issue(s)

Fixes #14178

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

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[vitess-bot]

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