Fix(preprocessing): resolve ValueError for ngrams tuple

[mykolaskrynnyk]

Resolves a deserialisation issue when ngrams is set to a tuple in TextVectorization layer. Closes #19180.

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[fchollet]

Thanks for the fix! Please add a unit test (so we avoid breaking it in the future...)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c8700f4) 80.14% compared to head (a077958) 75.48%.
Report is 38 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #19190      +/-   ##
==========================================
- Coverage   80.14%   75.48%   -4.67%     
==========================================
  Files         341      362      +21     
  Lines       36163    39049    +2886     
  Branches     7116     7564     +448     
==========================================
+ Hits        28982    29475     +493     
- Misses       5578     7948    +2370     
- Partials     1603     1626      +23     

Flag	Coverage Δ
keras	75.33% <100.00%> (-4.66%)	⬇️
keras-jax	59.46% <0.00%> (-3.60%)	⬇️
keras-numpy	53.92% <0.00%> (-3.17%)	⬇️
keras-tensorflow	60.81% <100.00%> (-3.85%)	⬇️
keras-torch	60.08% <0.00%> (-3.79%)	⬇️

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