Fixing varbinary (varbinary(XX)) schema migration for mysql to map to correct spanner type with length BYTES(XX)

[darshan-sj]

Fixes #<issue_number_goes_here>

It's a good idea to open an issue first for discussion.

• Tests pass
• Appropriate changes to README are included in PR

[shreyakhajanchi]

Please ensure the github actions pass before merging

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 3 lines in your changes missing coverage. Please review.

Project coverage is 43.66%. Comparing base (1af53bd) to head (c7d027f).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
sources/mysql/toddl.go	66.66%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1164      +/-   ##
==========================================
+ Coverage   43.64%   43.66%   +0.01%     
==========================================
  Files         227      227              
  Lines       26228    26236       +8     
  Branches      575      575              
==========================================
+ Hits        11448    11455       +7     
- Misses      14048    14049       +1     
  Partials      732      732              

Components	Coverage Δ
backend-apis	44.51% <ø> (ø)
backend-library	46.26% <66.66%> (+<0.01%)	⬆️
cli	22.40% <ø> (ø)
frontend	36.24% <ø> (+0.05%)	⬆️

Files with missing lines	Coverage Δ
sources/mysql/toddl.go	91.82% <66.66%> (-1.56%)	⬇️

... and 1 file with indirect coverage changes

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