Fix some "signed shift" warnings

[kevinbackhouse]

Fix some "signed shift" warnings flagged by CodeQL. In all of the cases that I have fixed here, it makes more sense to use unsigned types.

[codecov]

Codecov Report

Merging #2266 (b3f2ab5) into main (08a68c3) will not change coverage.
The diff coverage is 78.78%.

@@           Coverage Diff           @@
##             main    #2266   +/-   ##
=======================================
  Coverage   63.47%   63.47%           
=======================================
  Files         118      118           
  Lines       19604    19604           
  Branches     9556     9556           
=======================================
  Hits        12444    12444           
  Misses       5094     5094           
  Partials     2066     2066           

Impacted Files	Coverage Δ
include/exiv2/webpimage.hpp	100.00% <ø> (ø)
src/version.cpp	87.95% <0.00%> (ø)
src/webpimage.cpp	42.66% <28.57%> (ø)
src/types.cpp	94.47% <100.00%> (ø)

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