Update git2 dependency to 0.16

[mzabaluev]

Fixes:
https://github.com/informalsystems/tendermint-rs/security/dependabot/2

[codecov-commenter]

Codecov Report

Merging #1270 (fb11308) into main (5e46d85) will not change coverage.
The diff coverage is n/a.

❗ Current head fb11308 differs from pull request most recent head dca537a. Consider uploading reports for the commit dca537a to get more accurate results

@@          Coverage Diff          @@
##            main   #1270   +/-   ##
=====================================
  Coverage   64.3%   64.3%           
=====================================
  Files        250     250           
  Lines      21618   21618           
=====================================
  Hits       13920   13920           
  Misses      7698    7698           

Impacted Files	Coverage Δ
testgen/src/vote.rs	85.0% <0.0%> (-0.9%)	⬇️
testgen/src/commit.rs	90.6% <0.0%> (-0.7%)	⬇️
testgen/src/header.rs	83.5% <0.0%> (-0.6%)	⬇️
testgen/src/light_block.rs	87.5% <0.0%> (+0.5%)	⬆️
tendermint/src/block/commit_sig.rs	80.3% <0.0%> (+1.9%)	⬆️

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