[release-19.0] make sure to handle unsupported collations well

[systay]

Description

This is a backport of #15134

[vitess-bot]

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[systay]

Since we are in code-freeze, this needs to wait for #15139 to be merged first

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (release-19.0@020a082). Click here to learn what that means.

Additional details and impacted files

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##             release-19.0   #15143   +/-   ##
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  Hits                    ?   128807           
  Misses                  ?    53611           
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[frouioui]

Since we are in code-freeze, this needs to wait for #15139 to be merged first

Yeah I think it's best to merge this between RC1 and GA