Fix tests for OWSaveImage since wait_until_stop_blocking was replaced

[PrimozGodec]

Issue

In concurrent wait_until_stop_blocing is now replaced with wait_until_finished and tests started to fail.

Description of changes

wait_until_stop_blocing is now replaced with wait_until_finished

Includes

• [ ] Code changes
• [x] Tests
• [ ] Documentation

[codecov[bot]]

Codecov Report

Merging #172 into master will decrease coverage by 0.06%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #172      +/-   ##
==========================================
- Coverage   61.68%   61.61%   -0.07%     
==========================================
  Files          13       13              
  Lines        3236     3236              
  Branches      482      482              
==========================================
- Hits         1996     1994       -2     
- Misses       1116     1118       +2     
  Partials      124      124