Fix tests with recent Python (backport #2797)

[mergify]

This is an automatic backport of pull request #2797 done by Mergify.

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[codecov]

Codecov Report

Merging #2804 (7a0baf8) into 0.28.x (414bff1) will increase coverage by 0.05%.
Report is 59 commits behind head on 0.28.x.
The diff coverage is 54.54%.

@@            Coverage Diff             @@
##           0.28.x    #2804      +/-   ##
==========================================
+ Coverage   63.92%   63.98%   +0.05%     
==========================================
  Files         103      103              
  Lines       22306    22338      +32     
  Branches    10796    10821      +25     
==========================================
+ Hits        14259    14292      +33     
+ Misses       5827     5824       -3     
- Partials     2220     2222       +2     

Files	Coverage Δ
include/exiv2/image.hpp	100.00% <ø> (ø)
include/exiv2/matroskavideo.hpp	60.00% <ø> (ø)
include/exiv2/slice.hpp	90.56% <ø> (ø)
include/exiv2/value.hpp	85.11% <100.00%> (ø)
src/canonmn_int.cpp	72.88% <100.00%> (ø)
src/futils.cpp	73.09% <ø> (ø)
src/minoltamn_int.cpp	66.52% <100.00%> (ø)
src/panasonicmn_int.cpp	52.58% <ø> (ø)
src/pentaxmn_int.cpp	71.36% <100.00%> (+0.85%)	⬆️
src/rafimage.cpp	20.29% <ø> (ø)
... and 16 more