Polish C CHANGELOG for version 2.1.1

[gregorgorjanc]

Fixed the 2.1.1 version date typo and consolidated changelog entries (they were split into two entries with the same version).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.32%. Comparing base (11d9b60) to head (1859fd4).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #216   +/-   ##
=======================================
  Coverage   99.32%   99.32%           
=======================================
  Files           6        6           
  Lines         443      443           
  Branches       62       62           
=======================================
  Hits          440      440           
  Misses          1        1           
  Partials        2        2           

Flag	Coverage Δ
C	99.32% <ø> (ø)
python	99.32% <ø> (ø)

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[benjeffery]

Thanks!