fix version issue when using --mysql-shell-speedup-restore=true

[rvrangel]

Description

This change will make sure that we are correctly parsing the MySQL version beforing passing it to ServerVersionCapableOf(), otherwise we will get the wrong capabilities as in #18309.

Related Issue(s)

Fixes #18309

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 67.48%. Comparing base (2520f7f) to head (20eca39).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/mysqlctl/mysqlshellbackupengine.go	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18310      +/-   ##
==========================================
- Coverage   67.49%   67.48%   -0.01%     
==========================================
  Files        1603     1603              
  Lines      262428   262447      +19     
==========================================
- Hits       177114   177107       -7     
- Misses      85314    85340      +26     

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[deepthi]

nit: the test structure has changed, so this comment is no longer accurate.