test: Pinned Next.js tests to <16.0.0

[bizob2828]

Description

Next.js released 16.0.0 and there are some breaking changes that need to be addressed in our codebase:

• Our next.config.js needs to remove some options that are no longer supported.
• It looks like middleware is no longer supported, and we don't really support it as well, so we can remove that file.

I pinned for now as there may be more changes and i don't want to block CI.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.62%. Comparing base (b8678cc) to head (666c895).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3446      +/-   ##
==========================================
- Coverage   97.75%   97.62%   -0.14%     
==========================================
  Files         404      404              
  Lines       54575    54575              
  Branches        1        1              
==========================================
- Hits        53348    53277      -71     
- Misses       1227     1298      +71     

Flag	Coverage Δ
integration-tests-cjs-20.x	73.94% <ø> (ø)
integration-tests-cjs-22.x	73.98% <ø> (+<0.01%)	⬆️
integration-tests-cjs-24.x	74.66% <ø> (+<0.01%)	⬆️
integration-tests-esm-20.x	51.74% <ø> (ø)
integration-tests-esm-22.x	51.80% <ø> (ø)
integration-tests-esm-24.x	53.02% <ø> (ø)
unit-tests-20.x	88.47% <ø> (ø)
unit-tests-22.x	88.48% <ø> (ø)
unit-tests-24.x	88.52% <ø> (ø)
versioned-tests-20.x	80.89% <ø> (-0.33%)	⬇️
versioned-tests-22.x	80.89% <ø> (-0.33%)	⬇️
versioned-tests-24.x	80.83% <ø> (-0.33%)	⬇️

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