[projmgr] Ensure list target-sets accepts image-only solutions

[grasci-arm]

Address #2100
Complementary to #2138

[github-actions]

Test Results

    3 files     21 suites   12m 42s ⏱️
  399 tests   399 ✅ 0 💤 0 ❌
1 197 runs  1 197 ✅ 0 💤 0 ❌

Results for commit 658d59f.

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 4 lines in your changes missing coverage. Please review.

Project coverage is 66.10%. Comparing base (7638235) to head (658d59f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
tools/projmgr/src/ProjMgrWorker.cpp	0.00%	1 Missing and 1 partial ⚠️
tools/projmgr/test/src/ProjMgrUnitTests.cpp	80.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2143      +/-   ##
==========================================
+ Coverage   66.09%   66.10%   +0.01%     
==========================================
  Files         181      181              
  Lines       37306    37326      +20     
  Branches    21701    21711      +10     
==========================================
+ Hits        24656    24675      +19     
  Misses       8199     8199              
- Partials     4451     4452       +1     

Flag	Coverage Δ
projmgr-cov	80.58% <83.33%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
tools/projmgr/include/ProjMgr.h	100.00% <ø> (ø)
tools/projmgr/src/ProjMgr.cpp	81.86% <100.00%> (+0.24%)	⬆️
tools/projmgr/src/ProjMgrWorker.cpp	88.28% <0.00%> (+0.02%)	⬆️
tools/projmgr/test/src/ProjMgrUnitTests.cpp	80.49% <80.00%> (-0.01%)	⬇️

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