chore: remove upperbound of lz4_flex dependency

[gruebel]

Changes

• a new version of lz4_flex was released and the old one was yanked, which makes the upperbound unneeded now (Fix incorrect rust-version field name PSeitz/lz4_flex#187)

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.1%. Comparing base (b66b40a) to head (c43a208).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #314   +/-   ##
=====================================
  Coverage   53.1%   53.1%           
=====================================
  Files         64      64           
  Lines       9669    9669           
=====================================
  Hits        5141    5141           
  Misses      4528    4528           

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[lalitb]

Thanks @gruebel .